Three Amigos

A Power Trio of best friends, high school or middle school age, consisting of:
 * The Hero
 * A best friend of the same gender
 * A best friend of the opposite gender, 50% of the time an Unlucky Childhood Friend.

The two sidekicks will usually be opposites in other ways, too -- one will be a straight-A student, one will be a jock; or one will be rich, one will be poor; or one will be black, one will be white (or Asian). To that end, they may double as a Power Trio.

Romance will be explored. A Last Minute Hookup could almost always be expected between The Hero and a sidekick, until JK Rowling popularized the sidekick romance (although Lucas did it first with Han and Leia). One should hope that it won't turn into a Love Triangle.

The two sidekicks are almost always the Secret Keepers in a Wake Up Go to School Save The World setting. This is an attractive setup for many writers, because it gives the main character a person of each gender to interact with easily.

Most prevalent within American shows directed at children and tweens, where writers conspicuously try to keep their cast as limited as possible. Anime tends to add a fourth member, closer to one of the sidekicks than The Hero. They might also get a team expansion later, but the trio will always be front and centre and be treated like the "real" heroes.

Quite often the With a Friend And A Stranger dynamic will be present.

Is often Super Trope to Two Guys and A Girl, Two Girls and A Guy. Compare Token Trio. Contrast with the all-female Sister Trope, Beauty Brains and Brawn.

Terrible Trio is the villainous equivalent: The leader will be more bossy, and the sidekicks dumber and interchangeable.

Not to be confused with the comedy film. Or that one Disney film barely anybody remembers.

Anime

 * Samurai Pizza Cats: Speedy, Guido and Polly.
 * Angelic Layer: Misaki, Kotaro, and Tamayo.
 * Bobobo-bo Bo-bobo: Bo-bobo, Don Patch, and Tokoro Tennosuke (Jelly Jiggler in the dub) are known as the Hajike Trio.
 * Cardcaptor Sakura: Sakura, Tomoyo, and Syaoran + Mei-ling, Syaoran's Clingy Jealous Girl.
 * Even moreso in the manga, since Mei-ling is Anime-only.
 * Samurai Champloo: Mugen, Jin, and Fuu.
 * Yu-Gi-Oh: Yugi, Anzu/Tea, and Jyonouchi/Joey + Honda/Tristan, Jyonouchi's other best friend.
 * Yu-Gi-Oh GX: Judai, Asuka, and Sho + Hayato/ Kenzan, Judai's and Sho's other roommate.
 * Pokémon: Ash, Brock/Tracey/Cilan, and Misty/May + Max/Dawn/Iris.
 * Like the games, the main manga does this by the end of each region.
 * Kanto: Red, Green, Blue. Yellow takes over hero roles in her own arc, but doesn't offset the original dynamic during the Fire Red Leaf Green story.
 * Johto: Gold, Silver, and Crystal. Crystal was a late comer, but not as late as Emerald.
 * Hoenn: Ruby, Sapphire, and Emerald. However, Emerald didn't come in and complete the trio until after Ruby and Sapphire had done an entire arc.
 * Sinnoh: Diamond, Pearl, and Platinum.
 * Transformers Armada: Alexis, Rad and Carlos -- Billy and Fred were added later, but aren't really part of the trio dynamic.
 * Transformers Cybertron: Colby, Bud and Lori.
 * Digimon Adventure : Tai, Matt, Sora.
 * Sidekick romance becomes canonically in 02, they are married by the grand finale time skip.
 * Digimon Tamers: Takato Matsuki, Jianliang (Henry Wong) and Ruki (Rika Nonoka).
 * Eyeshield 21: Sena, Monta, and Suzuna. The hero, his best friend, and his love interest, with the latter two serving as secret keepers for part of the series.
 * Also Akaba, Kotaro, and Juri.
 * AIR: During Minagi's arc, there's Yukito, Minagi and Michiru.
 * Amatsuki: Toki, Kon and Kuchiha.
 * Amagami: Miya, Sae, and Ai
 * From Ikki Tousen: Teifu (Cheng Pu), Ryoumou (Lu Meng) and Saji (Zuo Ci) from Nanyou. But their friendship is horribly crashed when
 * Naruto, originally. (Naruto, Sasuke, Sakura)
 * All the Rookie Nine trios get this; as well as the older group (Neji, Lee, and Tenten).
 * Ranma One Half: Ranma (Hero); Ryoga (Best friend/Rival); Akane (love interest of both). Also, Akane loves Ranma but fights with him constantly; she is not in love with Ryoga and only sees him as her best male friend, and never fights with him. Ryoga loves Akane and Ryoga (until he moves on) and Ranma border on Vitriolic Best Buds. And that is the simplest, least psychotic romantic situation in all of the Ranmaverse.
 * Both Ryoga and Akane are heavily implied to be Ranma's best friends, completing the essence of this trope even more. It kind of makes sense seeing as how they're the ones he talks to the most about his problems or thoughts. At least it explains why fans ship Ranma with Ryoga and Akane so much.
 * Higurashi no Naku Koro Ni: Keiichi, Rena, and Mion are looked at as a trio. Satoko, Rika and Hanyuu may count as well.
 * Pandora Hearts: Oz, Gil, and Alice.
 * Code Geass has Lelouch, Suzaku, and Nunnally. Lulu is Nunna's brother, and Nunnally was hinted to have had feelings for Suzaku. Then it all went horribly, horribly wrong.
 * Soul Eater: Maka, Black* Star, and Death The Kid.
 * Though Soul, Tsubaki, Liz and Patti are always there also so I'm not sure it counts. If it does than Ox (with Havar), Kilik (with Fire and Thunder) and Kim (with Jaqueline) would be this as well.
 * Durarara has Mikado, Kida and Anri establishing this dynamic very quickly.
 * To elaborate:
 * Shigure from Fruits Basket said that himself, Hatori and Ayame were this during their school years.
 * Ouran High School Host Club has Tamaki and the twins, Hikaru and Kaoru. Or Tamaki, Kyouya, and the twins. Or Tamaki, Haruhi, and the twins... there are quite a few combinations, but the twins are closest to Tamaki and Haruhi (another reason why they tease and harass them, as opposed to the other club members).
 * Xamd Lost Memories has Akiyuki, Haru and Furuichi.
 * Star Driver has Takuto, Sugata, and Wako.
 * Sailor Moon during the first half of the first season, with Usagi, Ami, and Rei, before Makoto awoke as a Senshi and Minako revealed herself as Sailor Venus.
 * Arguably, Luffy, Zoro and Nami from One Piece. At the start of the series, they are surely this, being the only members that make up the Straw Hat crew, and even in the later chapters they have shades of this - Luffy is the absolute protagonist, and even though Your Mileage May Vary on this, Zoro stills seems to be the most important character in the series after Luffy (being his Number Two and all) and Nami is probably also the most important female character on the show. Their romance hasn't been explored in the series, though, but it is heavily discussed in the fandom, and some fans will insist that there are plenty of hints.
 * Except those fans are wrong, because Eiichiro Oda himself has stated that there will never be any romance among the main characters in One Piece, because he thinks it distracts readers from the main story. The only member of the crew who has a love interest is Usopp, who has Kaya waiting for him back at his home island. And even then, Kaya's not officially stated to be his girlfriend, but every time she's mentioned it's heavily implied that she's supposed to be.
 * Model Suit Gunpla Builders Beginning G has Haru, Kenta and Rina.

Comic Books

 * Trinity: Superman, Batman and Wonder Woman (Lampshaded in the first series arc, during which Wonder Woman even mentions her brief flirtations with both Superman -- the archetypal ideal husband -- and Batman -- the archetypal intriguing bad boy.)
 * Blue Beetle: Jaime, Paco and Brenda.
 * Legion of Super-Heroes: Cosmic Boy, Saturn Girl, and Lightning Lad.

Film

 * All Dogs Go To Heaven has Charlie, Itchy and Flo.
 * Starship Troopers: Johnny, Carl, Carmen; Johnny, Ace and Dizzy
 * Star Wars - Luke, Leia and Han Solo.
 * Spider-Man (2002)- Peter, Harry and MJ.

Literature

 * Harry Potter: Harry, Ron and Hermione.
 * The Pendragon Adventure: Bobby, Mark and Courtney
 * Percy Jackson and The Olympians: Percy, Grover, and Annabeth
 * And in the sequel series, Jason, Piper and Leo
 * ...and also in the sequel series, Percy, Frank, and Hazel.
 * Towards the end of the first Warrior Cats series, Firestar, Graystripe, and Sandstorm essentially become this.
 * The Dragonriders of Pern: F'lar, F'nor, and Lessa in the weyr; Sebell, Menolly and Piemur at Harper Hall.
 * Jem, Dill and Scout
 * The Princess Series: Danielle, Talia and Snow.
 * The Mystery Kids: Holly (Ego - the most normal one, uses reasoning to solve mysteries), Miranda (Id - prides herself on her ability to crack terrible jokes, most likely to be inspired to a solution), Peter (Superego - collects car registration numbers, loves technology and most likely to use a gadget to find a solution).
 * Green Sky Trilogy: Raamo (The Messiah), Neric (Deadpan Snarker), and Genaa (The smart girl)
 * The Three Musketeers (obviously): Athos, Porthos, and Aramis.
 * A to Z Mysteries: Dink, Josh, and Ruth Rose.

Live Action TV

 * Disney Channel is fond of this trope, and at least one show will have it.
 * Lizzie Mcguire: Lizzie, Gordo and Miranda
 * Hannah Montana: Miley, Lilly and Oliver
 * Even Stevens: Louis, Tawny and Twitty.
 * ANT Farm: Chyna, Olive and Fletcher.
 * That's So Raven: Raven, Eddie and Chelsea
 * Wizards of Waverly Place: Alex, Justin and Harper.
 * Cory in The House: Cory, Meena and Newt
 * The Famous Jett Jackson: Jett, JB and Kayla
 * Super Sentai has done this several times.
 * Choujuu Sentai Liveman: Yuusuke, Jou and Megumi.
 * Ninpuu Sentai Hurricanger: Yousuke, Nanami and Kouta.
 * Bakuryuu Sentai Abaranger: Ryouga, Yukito and Ranru.
 * Juken Sentai Gekiranger: Jan, Ran and Retsu.
 * Engine Sentai Go-onger: Sosuke, Ren and Saki.
 * iCarly: Carly, Sam, Freddie (with Spencer and Gibby as the fourth and fifth member respectively).
 * Ned's Declassified School Survival Guide: Ned, Moze and Cookie
 * Unfabulous: Addie, Gina and Zack.
 * Supah Ninjas: Mike, Owen, and Amanda
 * Naturally Sadie: Sadie, Margaret, Rain (Needless to say, Disney Loves This Trope)
 * Early Sabrina the Teenage Witch: Sabrina, Harvey and Valerie.
 * Buffy the Vampire Slayer: Buffy, Willow, Xander.
 * Early Smallville: Clark, Chloe and Pete.
 * What I Like About You: Holly, Tina and Gary.
 * Angel: Angel, Cordelia, Wesley.
 * Originally Angel, Cordelia, Doyle.
 * An increasingly popular Power Rangers format:
 * Mighty Morphin Power Rangers had Rocky, Aisha, and Adam before they were absorbed into the Five Man Band.
 * Power Rangers Ninja Storm: Shane, Dustin and Tori
 * Power Rangers Dino Thunder: Conner, Ethan and Kira
 * Power Rangers SPD does a fake-out with this trope: The ranger team starts out as Sky, Bridge and Syd, who fit the trope closely, but after Jack and "Z" arrive, they get rounded out to a Five Man Band by the end of the first episode.
 * Power Rangers Jungle Fury: Casey, Theo and Lily
 * Power Rangers RPM: Scott, Flynn and Summer (though they begin recruiting in episode 2)
 * Everwood: Bright, Colin and Amy in season one, mostly shown in flashbacks and the finale
 * True Jackson VP: True, Lulu, and Ryan
 * Boy Meets World has Cory, Shawn, and Topanga.
 * The West Wing: Josh, Toby, and CJ; after Sam left. Before he left, the whole ensemble was too tightly-knit to be separated into Amigos.
 * Degrassi the Next Generation J.T., Toby, Liberty. Jay, Alex, Sean. Marco, Ellie, Paige. In Fanon we have Spinner, Jay, and Holly J.
 * Season 10 seems to be hinting at Eli, Clare and Adam.
 * Early Edition: Gary, Chuck and Marissa.
 * Wishbone: Joe, Sam and David.
 * Unnatural History: Henry, Jasper, and Maggie
 * Doctor Who does it about half the time: The Doctor, a female companion to serve as The Heart and a male companion to serve as the Plucky Comic Relief or The Big Guy, depending.
 * Merlin has one of these, despite the setting. Arthur, Merlin and Guinevere don't attend high school, but they make up the aspects of the trope perfectly.
 * Greek has Evan, Cappie and Casey before the series began but it ended in it's logical conclusion, later they try several times to come back to this but they fail.
 * The Wonder Years: Kevin, Paul, and Winnie
 * Violet Vinther, Mr. Scwann and Miss Jørgensen from the danish Matador is this until
 * Battlestar Galactica Classic: Apollo, Starbuck and Boomer.
 * Starsky, Hutch and Huggy Bear.

Theatre

 * Evan, Patrice,and Archie in Thirteen.

Video Games

 * Lunar: The Silver Star: Alex, Ramus and Luna
 * The Tales Series is pretty fond of this:
 * Tales of Symphonia: Lloyd, Genis and Colette
 * Tales of Eternia: Reid, Farah, and Keele
 * Tales of Graces: Asbel, Sophie, and Richard
 * Streets of Rage: Axel, Adam and Blaze
 * La Pucelle: Tactics: Prier, Alouette and Culotte
 * Disgaea: Laharl, Etna and Flonne
 * Sonic Riders (Babylon Rogues): Jet, Wave and Storm.
 * Phoenix Wright: Ace Attorny: Phoenix, Maya, and Pearly.
 * Miles Edgeworth: Ace Attorney Investigations: Edgeworth, Gumshoe and Kay.
 * Professor Layton: Layton, Luke and Flora. (In the fourth game, which is a prequel to the three currently available in the United States, it's Layton, Luke, and Remi.)
 * Enchanted Arms: Makoto is the girl.
 * Broken up rather quickly.
 * Ogre Battle 64: Magnus, Dio and Leia.
 * Persona 3: The main character, Junpei and Yukari, at least early in the game before the whole team pulls together into a group of genuine True Companions. Mitsuru, Akihiko, and Shinjiro were Three Amigos in the early days of SEES, but fractured prior to the events of the game.
 * Persona 4: Main character, Yosuke, and Chie at first.
 * The lowerclassmen (Rise, Kanji and Naoto) may fit too.
 * Devil Survivor: Main character, Atsuro, and Yuzu
 * Fire Emblem is fond of this one:
 * FE4: Azel, Lex and Tiltyu; Sigurd, Cuan and Eltosian
 * FE6: Rei, Chad and Lugh
 * FE7: Lyn, Sain, Kent (Even though The Chick is also The Hero in this set up); Eliwood, Hector, Lyn; Wil, Rebecca, Dart
 * FE8: Ephraim, Eirika and Lyon; Tethys, Gerik and Marisa; Ross, Ewan, and Amelia
 * FE9: Ike, Titania, Soren
 * FE10: Elincia, Lucia, Geoffry
 * Both Jet Set Radio games have this: Beat, Gum and Tab in Jet Set Radio, and Yoyo, Gum and Corn (formerly Tab) in Jet Set Radio Future.
 * Kingdom Hearts: Sora, Riku and Kairi and Sora, Donald Duck and Goofy and . There's also Hayner, Pence and Olette and Terra, Ven, and Aqua and Roxas, Axel, and Xion. Something tells me Tetsuya Nomura is fond of this trope.
 * Elite Beat Agents: Agent J, Agent Morris and Agent Derek. On other difficulties, J is replaced by Agents Spin or Chieftain, and on the hardest difficulty, they are all replaced by cheerleaders (the "Elite Beat Divas").
 * Chrono Trigger: Chrono, Lucca and Marle of the 2 girls and a guy variant.
 * Final Fantasy VIII:: Laguna, Kiros, and Ward; Rinoa, Zone, and Watts; Seifer, Raijin, and Fujin for a villanous version.
 * Pokémon games after Generation II: protagonist, rival, and love interest/friend.
 * Metal Gear Solid: Guns of the Patriots gives us Snake, Otacon, and Sunny.
 * Planescape Torment: Although you can recruit other characters, the core trio are The Nameless One, Morte and Annah.

Web Original

 * That Guy With the Glasses: Spoony, Linkara and Marz Gurl.

Web Comics

 * Project 0 : Owen, Aatu, and Bea
 * Sluggy Freelance: Torg, Riff, and Zoe.
 * Almost every video gaming webcomic ever seems to revolve around two male gamers and one female, who is usually the girlfriend of whichever male lead is the hero. The typical character dynamic seems to be 'wacky' (read: obnoxious Jerkass) guy [The Hero], straight man [second guy] and girlfriend [the woman]. Oddly, the dean of video game webcomics, Penny Arcade, is actually the exception (no girlfriend), so Ctrl Alt Del is probably the Trope Maker here.
 * El Goonish Shive started out this way, with Elliot, Tedd, and Sarah, before the cast expanded.
 * Slightly Damned has Kieri (an angel), Buwaro (a demon) and Rhea (arguably the main character). Buwaro and Kieri are dancing around a romance.
 * Woods for The Trees has Jess (Male Border Collie), Reuben (Male Fennec Fox) and Isabel (Female Red Fox).
 * Mulberry from Platypus Comix has Mulberry (Non Idle Rich heiress), Jack (The One Guy), and Tiff (Dumb Blonde housekeeper).
 * Doodle diaries features a guy, his best/boy friend of the same gender, and his female Unlucky Childhood Friend
 * Something Positive: Davan, PeeJee, and Aubrey. Oddly Word of God has Jossed any romance between them despite the popularity and Ship Tease of Davan/PeeJee.
 * Samurai Princess has Princess Raeka, Jacquline and Lyonel. A girl and a boy about the same age who recently have been put in a situation of romantic tension and the little girl to play foil to the main character.
 * In Rescuing Dara Chivai is the hero and a girl, Dara is the female friend, and Zilch is the male friend. No romance yet, though.

Western Animation

 * American Dragon Jake Long: Jake, Spud and Trixie
 * Avatar: The Last Airbender Season 1: Aang, Sokka and Katara. Slightly unusually in that Sokka and Katara are siblings (and therefore have really similar experiences). Rather typical still in that they have very different personalities and capabilities.
 * The sequel series The Legend of Korra is slightly averted, as The Hero, Korra, is female and her friends, Mako and Bolin, are male. But like Katara and Sokka, Mako and Bolin are siblings.
 * Ben 10 Alien Force: Ben, Gwen, and Kevin
 * Danny Phantom: Danny, Samantha and Tucker
 * And the College Trio: Jack, Maddie, and Vlad.
 * Daria: Daria, Jane and Trent. In the fourth and fifth seasons and the movies, Trent is somewhat displaced by Tom.
 * Growing Up Creepie: Creepie, Chris-Alice, and Budge.
 * The school goth kids: Raven, Misery, and Morpheus, Creepie's other best friends of course.
 * The Emperors New School: Kuzco, Kronk, and Malina
 * Futurama: Fry, Leela, and Bender
 * Liberty's Kids: James, Sarah and Henri
 * Magi Nation: Tony, Edyn and Strag.
 * Megas XLR: Coop, Kiva and Jamie
 * Mucha Lucha: Rikochet, The Flea and Buena Girl
 * The Mysterious Cities of Gold: Esteban, Zia and Tao
 * Kim Possible: Kim, Ron and Monique. Although the trio dynamic is only really in play during the High School part of Wake Up Go to School Save The World, they have occasionally been involved in fights as a team.
 * But for the "same gender friend", the same dynamic works on the Save the World part, with Kim, Ron and Wade.
 * Pepper Ann: Pepper Ann, Nicky and Milo
 * The Spectacular Spider Man: Peter, Harry and Gwen. Played With when Harry is Put On a Bus for a while, with Mary Jane taking her place and remaining a sort of Fourth Ranger after he came back.
 * Roughnecks: The Starship Troopers Chronicles: Johnnie Rico, "Dizzy" Flores and Carl Jenkins.
 * Teamo Supremo: Crandall, Brenda, and Hector
 * The Wonder Pets has Linny, a gender-ambiguous female guinea pig that is supposed to be equivalent to a 5-year-old human child; a male turtle named Tuck, equivalent to a 4-year-old, and a female duck, equivalent to a 3-year-old, with a speech problem.
 * Wow Wow Wubbzy: Wubbzy, Widget, and Walden.
 * Hercules The Animated Series: Hercules, Icarus, and Cassandra.
 * Jimmy Two-Shoes: Jimmy, Beezy, and Heloise.
 * Jimmy Neutron, Sheen, and Carl may be all boys, but Sheen is dumb while Carl is smart, and Carl even called the trio the Three Amigops (a typo that he stuck with).
 * Tiny Toon Adventures: Buster, Hampton, and Plucky.
 * Babs, Shirley, and Fifi: A.K.A. 'The Amazing Three' in the cartoon short of the same name.
 * Once Upon a Forest had Abigail (the Tomboy), Russel (the Big Eater), and Edgar (the nerd). Subverted in that Abigail is The Hero and leader.
 * Time Warp Trio in the groups of Joe Sam and Fred/Jodie Samantha and Freddi.
 * The Three Caballeros, naturally.
 * Ultimate Book of Spells: Verne, Gus and Cassie.
 * Zevo-3: The pink-haired super hero Ellie Martin, Aka Elastika has 2 best friends, The gossip-girl Cotilla Vasquez and the goth-girl Angel Jones.
 * Aaahh Real Monsters: Ickis, Krumm & Oblina.
 * Braceface had Sharon, Maria, and Connor
 * Home Movies: Brendan Small, Jason, and Melissa.
 * The Simpsons: Bart Simpson, Milhouse Van Houten, and Samantha Stankey in one episode called "Bart's Friends Falls in Love". Lisa would fill Samantha's role on an occasional basis.
 * King of the Hill: Bobby, Connie, and Joseph.
 * Phineas and Ferb: Phineas and Ferb are best friends with both each other and Isabella.
 * Pretty much the whole point of Spider Man and His Amazing Friends.
 * Matt, Jackie and Inez of Cyberchase