Subverted in Goodfellas. Wise guys kill each other to save their own hides.
"Your killers come with smiles, as people you've known your whole life. And they always come when you are at your weakest"
In The Avengers (2012 version), at first the superheroes have significant differences, but Nick Fury (leader of SHIELD) deliberately tried to invoke this to bring them together in a time of need. It was a huge risk for him and his career. By the end he succeeds.
The plot of the Japanese film Densha Otoko (Train_Man) revolves around a true companions group that forms around the title character, a shy otaku who saves a girl from a drunk on the train. The true companions group is made up of people intrigued by his story, who encourage him and give him advice on how to woo the woman. He in turn inspires them to get out of the various ruts they have been stuck in.
Honey, I Shrunk the Kids: After going through several hardships in their shrunken state, the kids eventually warm up to each other, leading to a romantic bond between Amy and Little Russ.
The GSE, the West Ham United's firm, from Hooligans.
A variant on this pops up in The Maltese Falcon. If you're a detective, it doesn't matter that you hated your partner and were sleeping with his wife — he's your partner, and if he's killed you have to do something about it.
The cast of Zombieland, despite initial attempts to not form personal attachments to each other.
Danny Ocean's band in Ocean's Eleven, original, remake and sequels. Especially notable in Ocean's 13 where in the beginning much of the team wants to drug, kill, and bury the villainous casino owner who betrayed their friend and caused him to go into shock.
RENT has this when the seven friends band together in the wake of Benny's Face-Heel Turn, as well as the fact that half of them are HIV-positive. Even Joanne, an Ivy League lawyer who was only there because she was dating Maureen, gradually joined the gang and stuck around after the couple's breakup which was fortunate, since Angel's death brought them back together.
Since Newsies is about a strike, the importance of solidarity and sticking together is repeatedly emphasised, as in the song "Once and for All":
Once and for all we'll be there to defend one another Once and for all every kid is a friend, every friend a brother!
Todd Browning's Freaks centers on a group of circus "freaks," including a couple of folks with dwarfism, an intersex "half-man, half-woman," a pair of cojoined twins, a fellow with no limbs, etc. A "normal" trapeze artist marries one of the "midgets," and is treated to a wedding feast by his true companions, who cheer their friend's fortune, and welcome the aerialist as "One of us!" in the film's most memorable scene. When it's revealed that she only married him so that she could get to his money, kill him, and run off with her boyfriend, the pissed-off "Freaks" take revenge on her and the boyfriend, mutilating them and condemning them to a life as freaks, but without the solidarity of the others that made such a fate tolerable.
The cast of Sneakers appears, at the outset, to be employees at a small security firm, but when it comes time to circle the wagons, they work together like only true companions could.
The main protagonists in Robots, mainly between Rodney and the "Rusties".
Nowhere in any of the Star Trek movies is this shown more than in Star Trek III: after Spock sacrifices himself to save the Enterprise in the previous movie, the entire cast hijack the Enterprise, sacrificing their careers, possibly even their lives, along with the ship and Kirk's son in order to kill some Klingons and go after a one-in-a-million shot at bringing the green-blooded bastard back from the dead. This is driven home even further when, in the next movie, Spock chooses to stand with his "comrades" at their trial, despite not being charged of any crime himself.
Sure, they're rude, crude, and somewhat morally grey, but the Deltas from Animal House are definitely this. "They can't do that to our pledges! Only we can do that to our pledges!"
In the original Star Wars trilogy the core cast of Han Solo, Luke Skywalker, Princess Leia, Chewbacca, R2-D2, and C-3PO. Over the course of three films they risk their lives, endure torture and hardship, and make tremendous sacrifices for each other. Even the droids are treated like people instead of property, both of them being repaired after sustaining damage that most people would just consider an excuse to buy a new droid.
By Return of the JediLando Calrissian appears to be on his way to joining (he clearly views Han and Chewie this way, but it's less certain how he feels about the others and how they feel about him), along with possibly Wedge Antilles (moreso in the books than the movies, but the last scene of ROTJ shows him as part of the group).
Wedge is considered part of the true companions as far as the other characters are concerned, partly because he's one of the few left alive from the beginning. The problem is that he's the Hero of Another Story, so doesn't get to hang out with the rest as much.
One of the (many) complaints about theprequeltrilogy was that, in contrast to the original films, the main characters, in general, came across more as a group of people with similar goals than friends and family that cared about each other.
Consider also that this may be why the main characters fail to come together and defeat Palpatine. Teamwork, people!
The Vietnamese film Owl and the Sparrow revolved around one of these made up of three people who meet each other in Saigon: a zookeeper, a flight attendant, and a runaway girl who sells flowers on the street. The last scene of the movie has the flight attendant leaving the airport to meet the other two, hugging the little girl when she finds them
The main trio in the Harry Potter movies. The books have a lot more of them.
Thirteen Days: Kenny O'Donnell and Jack and Bobby Kennedy. They've known each other since college and Kenny gets very irate when he thinks an Obstructive Bureaucrat is trying to play them off each other.
Thor: Thor, Sif, and the Warriors Three are a pretty tight-knit group after adventuring and fighting together for thousands of years. Later on in the movie, Sif, Fandral, Hogun, and Volstagg risk everything to retrieve Thor from exile and are ecstatic when they're eventually reunited with him.
The 2011 film Sunny revolves around a woman reuniting her high school friends when one of them is dying of cancer. A good majority of the film takes place in flashbacks of them in The Eighties.
Stretch, Spoon and Cookie are true companions in Gridlockd. The group is a jazz trio who live together. Cookie has sex with both men, and the only reason they don't have threesomes is that Stretch says he can't get it up "in a crowd." Although both Spoon and Cookie are black, Stretch has N-Word Privileges with them. The group is so close that they all use the same bathroom at the same time.
"The Club"note Linda refers to it once as the "Johnny, Julia, Nick, and Susan Club", but thereafter calls it "The Club" for short. from Holiday. Linda initially conceives it as all of John and Julia's friends put together, but in practice it ends up being Linda, John, and John's friends Nick and Susan, with an extra chair for Linda's brother Ned. They identify themselves as Very Unimportant People with no interest in being snobs or stuffed shirts, who enjoy play, fun, and adventure, and who want to make money only insofar as it allows them to lead better lives. Julia declines to join them.
The Fast and the Furious team is this and is also one big happy surrogate family. It shows in Fast Five and Fast Six the most, but the bond is there. Dominic Toretto is the biggest example of this with his mantra of "You don't turn your back on family, even if they've turned their backs on you.".