Team Fortress 2/Shout Out

The list below is far from complete. The Official TF2 Wiki has a page of references, along with individual pages for each class. Several of those listed are Shout Outs.

"Scout: I. EAT. YOUR. SANDWICHES. I eat em up!"
 * One of the Pyro's taunts has him shake his flamethrower over his head with a muffled bellow, like the Tusken Raider does after knocking Luke out with his Gaffi stick in Star Wars.
 * Additionally, his/her taunt when equipped with the shotgun/flaregun is a classic Hadouken, complete with muffled call out.
 * The Spy achievements feature references to several influential spy shows and movies:
 * Burn Notice
 * Come in From the Cold (The Spy Who Came In From The Cold)
 * Point Breaker (Point Break)
 * Spies Like Us
 * The Man from P.U.N.C.T.U.R.E. (The Man From UNCLE)
 * The Melbourne Supremacy (The Bourne Supremacy)
 * Is It Safe? (Marathon Man)
 * James Bond films:
 * Die Another Way (Die Another Day)
 * Dr. Nooooo (Dr. No)
 * For Your Eyes Only
 * On Her Majesty's Secret Surface (On Her Majesty's Secret Service)
 * The Man with the Broken Guns (The Man With the Golden Gun)
 * You Only Shiv Thrice (You Only Live Twice)
 * The Sniper has an achievement called "My Brilliant Career" (an Australian film from 1979 starring Sam Neill).
 * One of the Heavy's hats strongly resembles that of a certain Hero of Canton.
 * During the Halloween event, there is a chance that when you taunt, your character would do the Thriller dance instead.
 * A hat was released as a Left 4 Dead 2 Preorder Bonus: Bill's beret.
 * Later, as another bonus to commemorate the release of The Sacrifice DLC, anyone who bought L4D2 before October 6th gained Ellis' cap for all classes and a frying pan weapon for the Soldier and Demoman.
 * Poopy Joe's is the Pickaxe that will pierce the vault of the heavens.
 * In "Meet the Demoman", an MIRV (the extra strong grenade from Team Fortress Classic used by Demomen and Heavies) can be seen in the back.
 * Several Demoman achievements, weapons, and battlecries are references to Highlander and Braveheart.
 * The Eyelander
 * His battlecry of "FREEDOM!"
 * "THERE CAN BE ONLY ONE!"
 * Some of the achievements include Bravehurt, Shorn Connery, Beat Me Up, Scotty, Laddy Macdeth, Something Stickied This Way Comes, and Left 4 Heads. Amusingly (or not, depending on your perspective), Left4Heads might also be a reference to the infamous porn video based on the first L4D game.
 * The Sniper has a bobblehead of the TFC "Hunted" (i.e. Civilian) model in his RV.
 * The Heavy often says his fists are made of steel. This is almost certainly a reference to when Rocky was fighting the huge Russian Ivan Drago. Drago says Rocky's fists are made of steel. Now Heavy's fists are made of STEEHUL!
 * With the release of some of the player-created hats, it really just begs for this. Brain slugs, for instance. The same update also gave us a nice Elvis Presley reference with gelled-up hair and sunglasses for the heavy, named "Hound Dog".
 * A handful of the voice clips that play when dominating a player reference the infamous milkshake seen from There Will Be Blood.

""Greetings, emissary from another dimension! We have heard your plea.""
 * Several items from Sam & Max were added as a bonus for players who buy The Devil's Playhouse. Cue Internet Backdraft, as Valve was selling out.
 * In the same vein, those who preordered or bought Worms Reloaded within the first week of it's release received the Lumbricus Lid for Soldier, which gave him a Worms style version of his standard helmet (complete with eyebrows), and two Holy Hand Grenades to replace his normal ones. A chorus sings out when he uses the Equalizer taunt.
 * The Medic has goggles in one of the community updates. Their name? Ze Goggles. To further the joke, their item description is "Nothing", and that was before new descriptions for other items poured in.
 * Ze Goggles, incidentally, are straight out of Ghostbusters.
 * The Dead Ringer announcement advertised that "reports of your death will be greatly exaggerated."
 * AI bots go by many names, including BoomerBile, TAAAAANK!, The G-Man, Black Mesa, The Freeman, GLaDOS, Companion Cube, Delicious Cake, Mentlegen, and Nom Nom Nom.
 * The Saharan Spy kit includes a knife called "Your Eternal Reward" (Additionally, it's function, killing the target, causing their body to vanish, and disguising the Spy as them, is markedly similar to the Stealth Consume from Prototype.), a revolver called "L'etranger", and a hat called the "Familiar Fez", a reference to a quote to Austin Powers: The Spy Who Shagged Me, where Austin told a fezed-mook from the first movie that he doesn't remember his name, "but [his] fez looks familiar.
 * There's also a Billy Joel song also called "The Stranger" about putting on the faces of other people and becoming a completely different person. Might just be a really convenient coincidence, though.
 * The Holy Mackerel's item level is always 42 for all players.
 * The Medic's Vita-Saw looks like the syringes the Little Sisters carry.
 * So much so that even though it was a community weapon, Valve went ahead and got 2K's permission before adding it.
 * The Carouser's Capotain was initially submitted under the name The Inquisitor, and while the name was sadly changed before final release, it still has the truly befitting description of "Suffer not a sentry to live".
 * When the Heavy taunts with the KGB equipped, he will perform several uppercuts in succession like Mr. Sandman in the NES version of Punch Out.
 * The Ad for Jarate from the Sniper vs Spy Update is based on This 1940's Advertisement.
 * The Sniper's parents are an Australian Eustace and Muriel! Confirmed by the artist herself. (It was a running gag in the fandom that his parents were Eustace and Muriel.)
 * Added in the Replay Update, the Team Captain hat looks suspiciously similar to the hat of a certain dictator. The description lampshades this by referencing the infamous scene from the Street Fighter cartoon: "Our Lawyers Say 'YES! YES!'"
 * Both Spy's talking, severed head and Medic's Halloween backpack with glowing green liquid inside are references to Herbert West.
 * A Summer Sale promotional item, the Summer Shades, is a reference to this fine fellow who lives up to the expectations Robin Walker sets for Australians.
 * The Halloween paper seal mask is an Ascended Meme: Someone misspelled "summer sale" in the official forums as "summer seal", and thus, a meme began.
 * In the replay update page, The Scout is pointing towards the screen in a similar manner to Mike/Joel's pose in most of the pictures of the
 * The latest Halloween update introduced a mutant fly costume set for the Engineer. Fittingly enough, the set is called The Brundle Bundle.
 * The update's backstory also has The (younger) Demoman reading the Bombinomicon while working as an apprentice for a magician.
 * The comic for the second Australian Christmas appears to contain a shout out to Engineer and Pyro fans, both of whom have received relatively few weapons compared to other classes.

"Try both being shout-outs to the ancient Greek Mathematician, Inventor, and philosopher."
 * An older version of Meet the Medic has a BLU Spy beg for death while the RED Medic is trying to kill him, phrased like a similar exchange in The Ark of Truth.
 * The Medic's dove being named Archimedes is possibly a shout-out to the owl in Disney's Sword in the Stone.


 * Amid other shoutouts already present, the Engineer's Gunslinger is quite similar to the Mini-Turret Glove from the Ratchet and Clank games. Given how off-the-wall TF2 is, it is right at home. Granted, the Mini-Turret Glove didn't require Ratchet saw his arm off. The engineer's Wrangler appears as an Atari 2600 joystick (more or less) and after a minute or so of continuous fire your character will work out the cramps in his hand as soon as fire is released which can only truly be appreciated by someone who played a 2600 game long enough to get a hand cramp.
 * The Spy can get a cool bowtie to wear. Its name is "Doctor Whoa". If you need more proof of what its referencing, it was released on the show's 48th Anniversary.
 * For added fun, wear the Familiar Fez with it.