Team Spirit

"I can tell you from experience that when they get along, it sucks muchly."

—Carl, the Evil Cockroach Wizard, Yin Yang Yo

On shows where the main characters are grouped together, goals ranging from winning games to defeating monsters are achieved only by teamwork.

A useful lesson, one supposes. It might be nice, however, to occasionally see a Too Many Cooks Spoil the Soup episode.

Examples of Team Spirit include:

Straight Examples

Notably Slayers, although Lina always seems to be the only useful member in the end.
Sailor Moon, especially the first season.
Futari wa Pretty Cure and Splash*Star (but not YPC5) take this to an extreme, in that its Magical Girls can only transform and make their magical attacks together (as in holding hands), so it's a good thing they know Kung Fu.
- Yes! Pretty Cure 5 does, however, focus on the team getting along. Strangely, it's the mature, Tall, Dark and Bishoujo Karen that causes all the problems.
Even more so, the eponymous airships in Simoun can only be operated by two girls working as a team...and they're powered by the pilots kissing each other.
The Space Squadron in Soukou no Strain takes great pains to integrate Sara into their Nakama and work together as a team. Although Sara goes solo against the Big Bad, she has the full backing and support of her team, who give her all the power they've got.
Eyeshield 21.
Digimon does this several times a season.
A running theme in the manga Kuroko no Basuke.

Every Star Trek series is built on this trope.
Stargate SG-1 and Stargate Atlantis.
Heroes took this to Anvilicious (but still enjoyable) levels in the episode, "How to Stop an Exploding Man" when every character teamed up to kick Sylar's ass and stop the nuking of New York.
Buffy the Vampire Slayer, particularly at the end of Season Four where the Scoobies use a spell that combines their powers into Buffy's body, and then kick the Big Bad's ass. It's pretty much Team Spirit given corporeal form.
While many of LazyTown's episodes revolve around the values of working together, there is one in particular that focuses on teamwork, complete with a song:

"Teamwork, do it together
Teamwork, friends forever,
We're all for one and one for all
We'll help each other stand tall,
With teamwork!"

This is the point of the pact system in The World Ends With You. Without a partner, a Player will get erased in a few minutes. And just to show how vital having a partner is, in the first day of the third week, you are drawn into a battle with Noise without a partner; you can still fight on the bottom screen, right? Wrong. All of your pins are disabled, leaving you with no choice but to run from battle.
Team Fortress 2's player classes all have different strengths, weaknesses, and unique abilities, forcing players to help each other out so their team can win...in theory, at least. There's also a hat-painting item known as Team Spirit, which makes your hat match your current team's color.

Rocket Power
The Powerpuff Girls. They did have a subversion of this cliche, however; see below.
Teamo Supremo
Teen Titans: Be it the Badass Normal or the Plucky Comic Relief, if even one Titan is absent....
The Weekenders: In "Sitters", the gang are babysitting Carver's younger brother... not surprisingly, they manage to keep things under control when they're working together.
Hey Arnold!: "Benchwarmer".
Yin Yang Yo: the two usually have to re-learn the Aesop about every other episode.
Used in Thomas the Tank Engine, particually in the later seasons where this seems to form the plot of half the episodes.
Wonder Pets: What's gonna work? Teamwork!
Mucha Lucha
Galactik Football
The Avengers: Earth's Mightiest Heroes has so many episodes where the Avengers save the day through teamwork, Loki caught the heroes in traps by forcing each to fight a Master of Evil alone.

The Powerpuff Girls: "Three Girls and a Monster" opens with the announcement that the City of Townsville has received an award for teamwork, and an example from the regular citizens being shown involving trash. However, Blossom and Buttercup are bickering over lots of things, picking up the hotline phone included. When the three girls finally meet the monster, one would expect the girls to defeat it by teaming up. Instead, Blossom and Buttercup continue to bicker while Bubbles gets the monster to leave town by asking nicely.
Hey Arnold!, "World Records": Might not have been an intentional subversion, but a subversion nonetheless. After several attempts by Arnold and Gerald to break a world record prove failures, Arnold comes up with the bright idea of getting all the neighborhood kids involved in making a giant pizza puff, using everyone's own special talent (Stinky's ability to wrap sleeping bags helps him fold the crust, Phoebe makes sauce, Gerald cuts vegetables). In the end however, that attempt is also unsuccessful, and their actual record comes from out of left field.^[1]
- They failed because one of the kids (forgot who) misinterpreted TSP—teaspoon—as Ten Square Pounds.