The Prince of Tennis: Konomi Takeshi has stated that the soon to be published continuation will deal with the formation of a "dream team" chosen from among the hundred or so best junior tennis players in Japan.
Averted in Air Master. The light-headed protagonist is portraying a generic Mook on a theme park, fighting some Sentai heroes. She beats the shit out of them without a thought, just by reflex. To avoid stopping the show and making their public sad, every member of the filming crew comes to the stage wearing costumes of an army of Kamen Rider-like old heroes. The dads of the children start cheering their youth idols. Airmaster then proceeds to kick every ass that gets too close to her.
Magical Girl Lyrical Nanoha A's features a semi-villainous Dream Team in the form of the Wolkenritter; ancient, immortal, reincarnating combat programs who are very good at their jobs.
Magical Girl Lyrical Nanoha StrikerS brings us Riot Force 6, which has such a ridiculously large portion of the firepower at the disposal of the Time-Space Administrative Bureau that they have to be placed under limiters before being allowed to operate together.
In Magical Record Lyrical Nanoha Force, Special Service Section 6 takes Riot Force 6, removes the limiters, and adds a large number of the Combat Cyborgs (who managed to actually challenge Riot Force 6) to the roster.
In Naruto we have the five Kages teaming up to fight Madara. Killer Bee and Naruto might also count as well, Sasuke and Itachi certainly do.
Kakashi and Gai during Orochimaru's attack on Konoha and in the current arc definitely count. On the evil side we have the Akatsuki, who is divided into dream teams (Even when the members do not get along). Itachi and Kisame stand out among those as the most badass team.
In Escaflowne, the Dragonslayers are an elite group of soldiers hand-picked by their leader, Dilandau. They are extremely loyal to him, even beyond the grave, despite Dilandau's habit of slapping them.
In Tower of God, Viole's new team, consisting of himself, Ran and Novick, Horyang, Cassano and some FUG members. Outright referred to as "a perfect team" by Novick. Averted when they get their asses handed to them by Leesoo's team.
Lupin III: The best thief, most deadly assassin, fastest gunslinger, and most beautiful woman team up.
Actually, by design, they more or less weren't, at least at first. DC established an in-house rule that any character who had (or later got) his own monthly title could no longer appear as an active member of the JSA (they could be "Honorary Members", though). Which made sense even in an in-universe way; a character with a monthly title was presumably busy with whatever adventures were appearing in that title. Superman and Batman thus started off as "Honorary Members," and Flash and Green Lantern (the Golden Age ones, Jay Garrick and Alan Scott) left shortly after the series began when they got their own titles as well. This rule was dropped after a few years, but originally it was thought of as a way to spotlight lesser-known characters and see if they were popular enough with readers to support a title of their own, instead of a "dream team" of the best of the best.
Marvel's Avengers is the Alternate Company Equivalent to the JLA Captain America, Iron Man, and Thor are the core of most incarnations. Hawkeye is usually on the team as well. Throughout the years the roster has consisted of a who's who of Marvel heroes, usually the most popular and most badass of whatever era the comic book is written in. Originally the Avengers weren't an All-Star Team like the JLA, but as time has gone on, this is what they've become. They're always the first response to planetary-level threats in the Marvel Universe.
Watchmen: Deconstructed twice. In "Under the Hood" (a book-within-a-book written by the first Nite Owl chronicling his time as a superhero) Nite Owl said that "it takes an extreme personality to put on a costume and fight crime and the chance of eight such personalities getting along is a million to one." Later when Captain Metropolis (a member of the last dream team, "The Minutemen") tries to form another Dream Team, "The Crimebusters", Rorschach complains that "...a group this size seems more like a publicity exercise, somehow it's too big and unwieldy." True to form, the group never gets beyond the initial meeting stage, as the personality clashes cause it to implode.
Kingdom Come features the new Justice League, Batman's army and Luthor's army. Plus Batman and Luthor team up!
The original Losers were essentially the war-comic equivalent of the Justice League, in that the team was made up of characters who had previously starred in their own features — Johnny Cloud, Captain Storm, and Gunner and Sarge (a double act, as it were). True to the concept, each one was incredibly skilled in certain fields, with Cloud being a peerless pilot, Storm a courageous leader, etc.
The Louisianna Gator-Boys from Blues Brothers 2000. Whatever you may think of the rest of the movie, that scene, at least, was cool - putting together a band of the greatest R&B musicians alive, just to counter the Blues Brothers Band's Power of Blues. The roster includes: B.B. King, Eric Clapton, Bo Diddley, Dr. John, Jeff Baxter and several other successful musicians — a true Supergroup.
The Great Escape: The Luftwaffe unintentionally creates an escaper dream team. Quoth Big X:
Bartlett: The men are here to do it. The Germans have put every escape artist in Germany in this camp, you said so yourself.
The Guns of Navarone. Each member of the team is the best at what he does: killing, explosives, mountain climbing, being lucky, etc.
Species. The team created to hunt down and kill Sil.
For the Rolling Stones concert film Shine A Light director Martin Scorsese assembled seven of among the best cinematographers in the industry just to operate the cameras at the Beacon Theater in NYC where the show was held.
The Dream Team: This Michael Keaton comedy movie spoofs this trope; the four main characters are dysfunctional psychiatric patients who have to overcome their various crippling neuroses, not to mention their inherent dislike for each other, to reveal the truth after they're framed for a murder by corrupt police officers.
The Expendables is an odd case, as it only fits the trope out-of-universe. In-universe, the Expendables are a very competent team, but they are not particularly noteworthy as individuals. In Real Life, they are composed of nearly every action movie star of the past 30 years, with the exception of Arnold Schwarzenegger (who had other commitments, but makes a cameo).
Until the finale of the sequel when Schwarzenegger joins the team as does Bruce Willis and Chuck Norris
In the book Rainbow Six Rainbow is an international anti-terrorist organization composed of former members of various special forces worldwide.
The Fellowship is part example, part parody. There's Gandalf, Aragorn, Boromir, Gimili and Legolas, which is a pretty cool team (a wizard, two human badasses, a dwarf and an elf). Then... there's the four Hobbits they're dragging around, even though they more than prove themselves later on.
In Changes, Harry Dresden pulls together a Dream Team to storm the Red Court stronghold in Chichen Itza, consisting of himself, Thomas, Murphy, Leanansidhe, Susan, Martin, Sanya, Molly, and Mouse. Also, half-way through the battle, Ebenezar and the Grey Council show up in a true Big Damn Heroes fashion. That accounts for pretty much every badass good guy/girl in the series and then some.
Older Than Feudalism: In The Bible (2 Samuel 23), King David assembled an elite squad of thirty "mighty men" to be his guard. All of them had impressive achievements in battle, including one who killed 800 Philistines in one day, one who singlehandedly defended an entire field, and one who "killed a lion in a pit on a snowy day."
The Belgariad features a kind of one. Belgarath assembles it based on "The Prophecy", but most of the members are considered noteworthy even in the Nation Of Hats they come from. There's Belgarath himself, "The Eternal Man," seven thousand year old sorcerer and emissary of a literal god; as well as his daughter Polgara, a powerful sorceress in her own right who is herself around three thousand. Silk is regarded as a top notch spy in Drasnia, which has as its main export intelligence (in the military sense). Mandorallen is from Arendia, a nation whose Hat is a knight's helm, and is considered its greatest warrior, having never lost a battle or joust. Barak is a Cherek (their Hat is a viking helmet), is an exceptionally strong berserker and captain of their largest warship, and can literally transform into a bear. Hettar, from Algar (think Mongols) can telepathically communicate with horses, and is spoken of with fear by his nation's hereditary enemies the Murgos, where legend has it that he's a thousand feet tall with a necklace of Murgo skulls. Garion is really Belgarion, the rightful Overlord of the West, though no one but Belgarath and his daughter Polgara, who are (distantly) related to him, know this at first. The odd man out at first is Durnik, who seems to mainly be there because he's a friend of Garion's (and of Polgara's in her disguise as Garion's "Aunt Pol"), but he turns out to be in the Prophecy as well.
Live Action TV
After they started replacing the entire cast with season seven, and up to the thirteenth season, Power Rangers would have the previous season's team return for one or two episodes to team up with their successors. Only the eleventh season wouldn't feature the previous cast return in this period.
On the other side of the pacific, Super Sentai, the Japanese franchise that provides the source material for Power Rangers, has been making crossover movies between teams starting with Ohranger vs. Kakuranger, (although there has been previous crossovers before the official Vs. movies). Usually these crossovers tend to involve the current team and the previous team, but for two of the anniversary years (the 25th and the 30th), the current team worked together with a mixed team of various past heroes instead.
In Kaizoku Sentai Gokaiger, the 35th Sentai series, the team has the ability to transform into previous heroes. Usually the Gokaigers will all stick to rangers from the same team, but sometimes they transform into mixed teams as well, particularly when they have all have a common motif or they have the same color.
Gokaiger Goseiger Super Sentai 199 Hero Great Battle takes it [[Up to Eleven]], beginning with all the rangers that ever were teaming up and sacrificing their powers to defeat a fleet of Zangyack... creating the keys that allow the Gokaigers to transform into newer forms when they come along later. The movie's climactic battle features all the main mecha that ever were smacking down a handful of resurrected recent villains.
Whenever Doctor Who does a story with more than one Doctor appearing (The Three Doctors, The Five Doctors, The Two Doctors, "Time Crash"), Doctor Who is in something of a unique position in that it's essentially a 'dream team' comprised of what is essentially different versions of the same character. Brought Up to Eleven (and beyond) in the 50th anniversary special, where all the Doctor's incarnations up to and including the Twelfth work together to save Gallifrey. Day of the Doctor indeed.
A Supergroup is the music version of a Dream Team.
Quincy Jones, mainly remembered today for "Soul Bossa Nova" (the theme of the Austin Powers films) and the soundtrack to The Fresh Prince of Bel-Air, released his opus Back on the Block in 1989. The album featured the crème de la crème of the black pop, R&B, soul, jazz and rap scenes, for its time. Over 100 contributors are cited throughout the liner notes, including Miles Davis, Ella Fitzgerald, Sarah Vaughan, Ray Charles, Barry White, Melle Mel, Herbie Hancock, Rod Temperton and Greg Phillinganes (best remembered for all of the synth work on Michael Jackson's Off the Wall and Thriller; Phillinganes also developed a lot of Stevie Wonder's synths during the 70s and 80s) and even Jesse Jackson. The album went on to win seven Grammys, including Album of the Year.
The Trope Namer is the 1992 American men's Olympic basketball team (specifically a 1991 Sports Illustrated article about the team by Jack McCallum). The Americans had always been dominant in basketball at the Olympics, sending college basketball players to comply with amateur requirements. But a bronze medal in 1988 was embarrassing enough that for the first time NBA players (and Christian Laettner) were selected for the 1992 team after the International Basketball Federation opened the games to pros. It was almost certainly the greatest collection of talent ever assembled on one basketball team—and quite possibly any sport—with at least three players (Magic Johnson, Larry Bird, and Michael Jordan) often considered the best in their positions to ever play. Eleven of the twelve team members are in the Basketball Hall of Fame, and the twelfth—Laettner—is considered one of the greatest college players of all time and went on to have a successful NBA career himself. Coach Chuck Daly remarked that it was like "Elvis and The Beatles put together"; Bird joked that if they lost they "probably wouldn't be allowed back in the country." They won by an average of almost 44 points; the closest game saw them win by 32 against Croatia (who expressed gratitude to win the Silver medal before the game was even played).
The team lost one game ever: their first practice (against a group of college all-stars), which one of the other coaches said Daly deliberately threw (by limiting Jordan's playing time and making non-optimal substitutions) in order to prove to his team that they could be beaten.
The above team may have met their match with the 2012 Olympic team, which consists of many modern-day NBA All-Stars, including Lebron James, Kobe Bryant, Chris Paul, Kevin Durant, Carmelo Anthony and Andre Iguodala.
Similar rule changes allowed NHL players to compete at the Winter Olympics. Since the NHL has far more international players than the NBA, this results in an entire tournament full of Dream Teams.
In a real life/media crossover, the "Les Miserables - The Dream Cast in Concert" recording pulls (theoretically, and in many cases widely-accepted) the best performers for each role, from Broadway, London, and Australia, for one performance.
You can make this happen yourself in Backyard Sports, as you choose your players (many of which are some of the best players in the leagues).
By the end of the game, any given Super Robot Wars's cast will become this, with the combined forces of numerous Humongous Mecha series teaming up to defeat a new threat after all their storylines have finished.
Some of the best people from Enix hired themselves out to Square to make Chrono Trigger, along with Akira Toriyama, and actually used the name "Dream Team" for themselves in the Developer's Room.Chrono Cross was also made by the Dream Team, but without Toriyama. Sadly, and more than a bit confusingly, nothing similar has happened since the two companies merged.
Most any party-based RPG ever involves this at some level. Even when they're a Ragtag Bunch of Misfits, you do end up saving the world in the company of some of the best-qualified people in it.
Most of the plot of Fable II revolves around assembling a Dream Team so that a prophecy will oust a horrible tyrant. The Player Character must track down and unite the Hero of Strength, the Hero of Will, and the Hero of Skill, which is harder than it sounds.
Inazuma Eleven, the game more than the anime. Though the anime team is made of several of the best players defected from other teams, the game explicitly encourages you to find and recruit the strongest players from any team you battle, making the ultimate team a mishmash of the cream of the crop.
GO Chrono Stone features a dream team made up of historical figures that was envisioned by Endou Daisuke as the ultimate team. This leads the team to travel through time to gather the power of these memnbers. The first of which is Oda Nobunaga.
Axe Cop is what happens when a supremely imaginative six-year-old boy's ideas are taken up by his brother, a supremely talented twenty-nine-year-old comic book illustrator.
While Team Kimba of the Whateley Universeis a Dream Team, most of the school believes this trope is in play because Phase is a teen billionaire who as a Goodkind would pull together a dream team as his personal backup. He just happens to have one of the best mages in the world, one of the best flying bricks available, one of the best (if not the best) flying blaster, one of the best martial artists anywhere, plus the Handmaid of the Tao and the Crazy Awesome Generator.
Hanna-Barbera's Laff-A-Lympics was a dream team.....of funny. The "classic" Hanna-Barbera "animal" characters were all on one team (captained by Yogi Bear), the "modern" Hanna-Barbera "crime-solver" characters were all on another team (captained by Scooby-Doo), and the "Devious" Hanna-Barera "villians" from both eras (captained by Mumbly) - all on one cartoon!!
Total Drama All Stars had the the heroic and the devious characters from the past four seasons join forces.