Abenobashi Mahou Shoutengai: After the first episode, the heroes fall from world to world, each one based on one of the main characters' geekish hobbies.
The main premise of Arata Kangatari; Arata of the Himezoku is transported to modern-day Japan, while Arata Hinohara is trapped in the world of Amawakuni.
Aura Battler Dunbine, but then it twists it by having all the people from the other world get sent to Earth.
The Wings Of Rean, made by the same director and in the same setting, is like-wise, although both are more like "people from Earth get sent to another world who then get sent back to Earth and then get stuck there with otherworlders."
El-Hazard: The Magnificent World: When Ifurita sends Makoto to El-Hazard, and accidentally sends along Fujisawa-sensei, Jinnai and Nanami as well.
In Fullmetal Alchemist, the first Homunculus is trapped in the human world and in a flask, which he admits sucks, but he's not that bothered about it. Later he tries to use the human world to "eat" the entity that controlled him in his world. Ironically, he ends up trapped in his own world, presumable tortured for eternity.
In Fullmetal Alchemist: Conqueror of Shamballa, in an inversion, they are trapped in our world, having originated from another, where magic alchemy is fairly commonplace.
Fushigi Yuugi: Miaka and Yui get pulled into a mythical world inside a magical book. The same thnig happened to their predecessors, Suzuno and Takiko.
Kyou Kara Maou: Though Yuuri isn't really trapped, and can go back and forth between the two worlds with relative ease, he only considers himself trapped when he returns to his native world.
Jura Tripper sends no less than 15 people to a planet where humans and dinosaurs co-exist.
The Twelve Kingdoms: Youko Nakajima and her friends Ikuya Asano and Yuuka Sugimoto get dropped in the middle of a mostly hostile fantasy world by a White-Haired Pretty Boy/Mysterious Protector. Though, this is apparently common enough for the locals to coin terms ("Kaikyaku" for Japanese people, "sankyaku" for Chinese) and for the government to have a regular policy in dealing with them. For example, The Kingdom of En has a standard naturalization/citizenship process while Kou just tries to round them up and kill them.
And before they came in, a farm girl named Suzu was spirited away from the Meiji era and thrown in the same world. Only to go through much heartbreak.
Shoryu, the king of En, also was from Japan. In fact, he was a daimyo or feudal lord whose clan was wiped away in the feudal wars. Having become a Fallen Prince, he accepted to become the King of En.
Vision of Escaflowne: A rare example of the other world not being treated as another dimension of some sort — they get stuck on an invisible moon, just past the actual one.
Now and Then, Here and There (aka Ima Soku Ni Iru Boku). This is an exceptional example of this trope because the creators threw out every convention associated with it from episode 1. Shu sees a strange young girl sitting on a smokestack on his way home from school and goes to meet her. As he is introducing himself he and the girl are attacked by people teleporting in from the distant future in pursuit of that girl. True to the genre Shu picks up a stick and fights to defend the girl. He immediately gets his ass handed to him and both he and the girl are dragged forward billions of years where Earth is a dying desert planet orbiting a sun in the early stages of nova. What follows is a relentless thirteen episode trip through the ninth ring of Hell.
Kagome from Inu Yasha in the first few episodes. Afterward she's able to go between the other world and her own at will.
Subversion: Yukinari from Girls Bravo gets trapped on the planet Seirun in the first episode, but is returned to Earth in the same episode.
Spider Riders plays with this, Hunter never seems to feel like he's "trapped" in the Inner World. The reason he ended up there in the first place is because he went looking for it!
The Mahou Sensei Negima! manga has Negi and a group of his student get stuck in the Magic World after Fate destroys the gateway between worlds.
Those Who Hunt Elves do so because the elves hold the secret to the spell that will return them to Earth.
In Zero No Tsukaima, the male protagonist is "accidentally" summoned to another world by the female protagonist in a summoning ceremony.
Long-running shoujo series Red River and Ouke No Monshou both feature this trope, a girl from modern day trapped in Ancient Mesopotamia and Ancient Egypt respectively.
The Sorcerer's Curse arc of Mythic Quest revolves around everyone in the world being deposited in the dimension created by the MMORPG Mythic Quest with no way out and no extra lives.
This happens to Tsukasa from .hack//SIGN, with a computer game.
In There, Beyond the Beyond, protagonist Futaba is taken to a fantasy world due to a case of Mistaken Identity. In order to get back home, he needs to reunite the Amaranthine with her master.
Ginta of MÄR actually makes the willing decision to go to the other world (after wordlessly making sure his love interest is unable to follow him), and once there is overjoyed to find that getting back isn't going to be easy.
The main plot of the (awful) hentai, Slave Warrior Maya, where a young woman is magically sent to another world and then tricked into undressing so she can be sold into slavery.
Occurs frequently in Digimon:
Digimon Adventure starts with seven kids being unwillingly transported to the "Digital World", a dimension full of sapient creatures somehow created from data in the real world. The kids initially have no idea how to get back.
Digimon Tamers has the protagonist kids purposefully travel to the Digital World in an attempt to rescue someone, but they are left uncertain of how to return to the real world.
Digimon Frontier, much like Adventure, starts with a group of kids being transported (somewhat willingly, there is a Call to Adventure beforehand) to the Digital World without knowing a way to get back.
In Dog Days, the people of Biscotti summon Cinque to help them, but then find that they don't know how to send him back to Earth. This no longer becomes an issue once they find the return spell.
In a short hentai Enslaved in Unknown World a teenage boy was naked, about to take a shower, when he found himself in a strange world. Where he's imprisoned, tortured, and raped by the men. Then he ends up being auctioned with a permanent boner.
CrossGen's Negation featured a Ragtag Bunch of Misfits trapped in an alternate universe that did not obey the laws of physics. At least one character started out convinced that it was All Just a Dream.
This is the raison d'etre for the Marvel comic series The Exiles. Superpowered beings lost from their dimension, world hop until they get to go home.
This was Adam Strange's origin in DC Comics. An archeologist who accidentally discovered an alien transport system, Adam became the number one hero of the planet Rann. His problem was that the Zeta beams which teleport him are only temporary and he has started a family on Rann. He has since been able to stay there permanently, but on occasion where he finds himself on Earth and this trope applies there.
Dungeon Keeper Ami features this prominantly- with something of a twist. The Light Gods are capable of sending Ami back at any time, and Ami is aware of this fairly early. However, due to Ami's unfortunate bonding with a Dungeon Heart, they refuse to do so. Rightly so- if she returned to her world with a Dungeon Heart, she would inadvertently draw the Dark Gods after her. The story evolves around her attempts to discover a way around this.
An excellent example of this trope in fanfic is With Strings Attached. The four are scooped up and dropped on the planet C'hou with nothing except the clothes on their backs and some musical instruments; they're terrified out of their minds and have absolutely no idea why they're there. The reader knows they're there as the subjects of an alien undergraduate psychology experiment (at least initially, until the experiment breaks down), but the four don't learn anything for around a month, when they're told that they've been brought over and equipped to fetch the three pieces of a statue to end a continent-sized curse. The quest is legitimate in context, but was assigned to them after they were equipped.
Fans of The Lord of the Rings often write about girls falling into Middle-earth. These girls, and some boys, come from our modern world. With the film adaptation, there appeared a veritable storm of such stories.
These fanfics tend to be mediocre to terrible. Nearly every single one of these girls is a Mary Sue in the guise of an Ordinary High School Student, who is more often that not a self-insert that falls in love with Legolas or, less commonly, Aragorn, as Wish Fulfillment for her author. A common trick is to transform the girl into an elf or a hobbit, to match her love interest. The inserted girl is usually a fan of the movies, and has foreknowledge of events; she might also recognize characters on sight, implying that they look exactly like their actors in the movies.
Most authors use the same three conveniences. First, the inserted girl lands conveniently near major characters. She often lands near the Council of Elrond, because that is the first scene with Boromir or Legolas. Second, she can chat in English, because the author forgot that the Common Tongue is a different language. Third, she never tries to return home, because she likes living in Middle-earth.
Time Will Tell is this done by a fan of the books. Jorryn from America appears in the Shire, and ends up living with Bilbo and Frodo. When Frodo must leave the Shire, Jorryn goes with him. Time Will Tell brings Jorryn through the Old Forest and to Tom Bombadil, in events from the books but Adapted Out of the movies.
Home With The Fairies is a deconstruction. Maddie lands in Middle-earth, but she is lost. When she finds a town, she hits a Language Barrier because no one speaks English or knows anything about America, her home. She almost dies, and lampshades the Plot Armor that seems to keep her alive. Unlike most of these characters, Maddie also wants to find a way home.
Let us just say that Fan Fic writers LOVE this trope when they do crossovers, self-inserts, etc. It's a very common trope for Fan Fiction. So much so that it has its own Fan Nickname: "Bamfing".
This has become the franchise staple, as no protagonist gets digitized voluntarily. In Tron 2.0 Jet Bradley gets digitized by Ma3a in a desperate act of self-preservation. Later, The F-Con thugs forcibly shoot Alan in there, too. In TRON: Legacy Sam learns the hard way that you shouldn't press "yes" at every pop-up dialog on a somebody else's system.
In Cool World, both Frank and Jack are transported to the titular world.
Literature
L. Frank Baum's The Wonderful Wizard of Oz. Most of the first six-odd "Oz" books fell under this trope, with Dorothy finding her way back to Oz only to get back to Kansas by the last page, though eventually Baum just had Dorothy (along with Uncle Henry, Aunt Em, and Toto) move to Oz full-time and continue her adventures there. Whenever another human came to Oz from the outside world after that point, they generally ended up staying (Oz after the wicked witches died and Ozma took the throne being a much more utopian place to live, occasional monsters and baddies notwithstanding). It's implied even pre-Ozma that Oz was a much better place to live than Kansas; and Dorothy only kept going back home because she didn't want to ditch her family. That certainly is her only reason after meeting Ozma, whom she has a very close relationship with.
In Diana Wynne Jones's Charmed Life this is what happens to Janet and her eight analogues in the other worlds in Series Twelve - when Gwendolen escapes from World 12A, she pulls Janet in from World 12B, and so on all around the circuit. Janet is the only one who doesn't find the change to be an improvement, and when she realises this, decides to stay in 12A for the sake of the others. Janet's parents don't notice the change.
Guy Gavriel Kay's The Fionavar Tapestry. The five main characters are transported to Fionavar at the beginning of the first book, The Summer Tree and return to their own world at the end of it; then they go back near the beginning of the second book, The Wandering Fire, and stay there through to the end of the third, The Longest Road, when their various fates are resolved. At the end of the trilogy the score stands with two going back to our world, one choosing to stay in Fionavar, one dead in a Heroic Sacrifice, and one sailing off to eternity with Lancelot and King Arthur as she is, in fact, Guinevere. The books are somewhat eclectic.
C. S. Lewis's The Lion The Witch And The Wardrobe; a slight twist here is that the characters age significantly during their stay in Narnia, then are returned to their original ages when they leave. The other Narnia books tend to follow this pattern as well, except for The Horse and His Boy.
In Alan Dean Foster's Spellsinger series, the main character is summoned by a powerful wizard looking for another powerful wizard. Apparently, an engineer would be the closest thing to the alternate world's wizards. Unfortunately, the summoning spell latched on to the main character's job title...sanitation engineer. Fortunately, he does turn out to have magical abilities in that world.
Similarly, in L. E. Modesitt Jr's Spellsong Cycle, the main character is summoned because of her skills as a singer. The author seems to like this trope, since in his Saga Of Recluce series this combined with Lost Colony is used in two books.
Actually inversed with The Princess 99, where an alien biker chick from the future finds herself stuck in the human world in the 1920s.
Barbara Hambly's Darwath series: Ingold could bring Gil and Rudy back to Earth any time, at the risk of the Dark learning how it's done and coming to eat Los Angeles. By the time the threat of the Dark goes away, so does our heroes' desire to go 'home'.
Joel Rosenberg's Guardians of the Flame series depicts a small group of college students who get magically transported to the world of their fantasy roleplaying campaign. They struggle to escape but decide by the end of the first book to stay in their new home to wipe out slavery.
The Summoning series by fantasy/romance author Robin D. Owens focuses on a group of Colorado women who are called, one by one, to be champions of the world of Amee. Unique in that any Earth-native brought to Amee will eventually face the Snap ... a point where Earth tries to call the person back, and will unless she has made a stronger commitment to Amee.
The premise of The Inverted World is that a city has somehow become transported to a bizarre alternate world, one where they must constantly move forwards in order to survive.
Land of Oblivion has its Kid Hero protagonists transported to a place where dead children have their afterlife. The place is not all rosy, though, and they have to save the girl's brother from becoming Deader Than Dead.
Coraline is somewhat a Deconstruction of this concept, as the other world literally is a Trap for her (and others) - and nothing more. Unlike most examples, The heroine is very glad to leave it behind.
Dave Duncan's The Great Game explains why characters in this situation tend to become heroes—anyone who's in a different dimension than the one they were born in can absorb Mana. At low levels, this just makes them really, really charismatic. If they convince other people to make sacrifices to them (usually of blood), they can become Physical Gods. All "godly" beings in this dimension are actually from our world.Therearehazardsto this, however . . .
In Warrior Cats, Jayfeather is stuck in the past until he can turn the Ancients into the Tribe of Rushing Water by teaching them tribe customs.
In Daughter of the Falcon, Jessie, a girl from our world is trapped in Mysteria, a Magical Land. This is then Deconstructed as she needs insulin injections and there is nothing comparable in Mysteria, so unless she can return home, she will die when her supply runs out
In Sergey Lukyanenko's The Boy And The Darkness, the protagonist is a teenager named Danny who travels to another world covered in perpetual darkness. His way home is almost immediately destroyed. The other two portals get destroyed later. At the end, Danny gets the chance to go home by wishing for one thing from a godlike being. He uses the wish to save a friend rather than return home.
H. Beam Piper's Lord Kalvan of Otherwhen was once a Pennsylvania state policeman named Calvin Morrison, who was accidentally dropped off in a parallel universe where the Aryans went east instead of west, and conquered North America. As it happens, he lands in a small kingdom that's about to be wiped out by the Corrupt Church that holds a monopoly on the secret of gunpowder manufacture...and he knows how to make gunpowder.
Grand Central Arena: The experimental starship Holy Grail and its crew find themselves stuck in The Arena, a vast extrauniversal construct, and can't get back home unless they learn how the rules of The Arena work. Unlike most of the other examples, this one is SF, not fantasy, although there is Sufficiently Advanced tech involved.
In Teresa Frohock's Miserere: An Autumn Tale, going through the Veil to the Woerld means you can never return to Earth.
In Dirge for Prester John, getting into or out of Pentexore is impossible most of the year, effectively trapping anyone who isn't keeping a strict eye on the Rimal.
The titular Id finds himself trapped in a world he has absolutely no knowledge about and has no idea how he got there - but where he comes from is another mystery.
Once you have entered Palimpsest once, you will go there whenever you have sex, whether you want to or not.
The original, that is. The American version was much less ambiguous.
Doctor Who: Rose is trapped in a parallel world, but returns with knowledge of "the Darkness" threatening to destroy the multiverse (as her universe is ahead of ours). She is then forced to remain in her parallel world to take care of the clone-Doctor, despite wanting to stay with the real one. Former boyfriend Mickey, however, decides to leave the parallel world for his old one.
Farscape, where Crichton travels through a wormhole to another part of the universe. His overriding goal for most of the series is to get back to Earth...but when he finally does, he leaves very shortly to go back to the other side of the universe. He later returns and makes it impossible for himself to ever go back in order to protect Earth from the bad guys. John, being John, makes many a reference to The Wizard of Oz in relation to his situation. Title of the episode when they really go to Earth: Kansas.
The Time Tunnel - two guys trapped in the past (or occasionally the future).
Season 1 of Stargate Atlantis — trapped in the Pegasus Galaxy. This is a variation, because the expedition went to Atlantis knowing full well that they might be stranded there.
Stargate Infinity — generally trapped away from Earth and the rest of polite galactic society since their iris codes had been revoked.
According to early reports, Stargate Universe is taking this tack as well, stranding the heroes on a space ship headed away from known space
They are billions of lightyears away from home and if they could control the ship, the journey would take millions of years. They don't have enough power to dial home and dialing IN from the Milky Way needs a special kind of planet but even then, a small mistake in the calculations WILL cut off the supply line permanently via an Earth-Shattering Kaboom. This happened in the first episode. Later on, it was revealed that the Lucian Alliance found another planet which the SGC attempted to capture; the Alliance however activated the gate prematurely and this planet blew up as well.
The island of LOST is sufficiently weird that a case could be made.
This happens a lot in the Polish/Australian children's series Spellbinder. Paul gets trapped in the Spellbinder universe, Kathy's family gets trapped in the Land of the Dragon Lord, and Mek and Kathy end up trapped in first the Land of the Immortals and then the Land of the Moloch.
In Kyle XY, Josh frequently suggests that Kyle is an alien from another world (although this is later subverted when Kyle's true origins are revealled).
In season 3 of Fringe, Olivia is trapped a good deal of the time in another universe, an alternate universe. Peter has been trapped in another universe since he was seven years old.
Angel, where Cordelia was trapped in Pylea and ended up becoming queen and overthrowing the priests. Fred was stuck there too, though she didn't do nearly as much as Cordy.
In the first episode of MythQuest, Matt Bellows gets trapped inside a mythical world with a trickster god. His children accidentally (and later deliberately) get trapped in myths when they go to look for him.
Once Upon a Time is an Inversion - the fairy tale folks were dumped in our world by a curse
Radio
At a book signing, Sam from Elven Quest is dragged into LowerEarth when a group of heroes kidnap The Chosen One, aka. Sam's dog, and he wouldn't get them go. Naturally the only way to get back is to go on their quest to get the Sword of Asnagar, which will (a) defeat the Lord Of Darkness and (b) let Sam go back home).
Video Games
Dragon Quest III. Combines alternate dimension with Time Travel, as Your hero turns out to be the legendary Roto, heroic ancestor of the heroes of the previous Dragon Quest games. This also means that 90% of the game is the prologue.
The Pokémon Mystery Dungeon games combine this your character being a human stranded in a world full of other talking Pokemon, transformed into a Pokemon themselves.
Nox, with the protagonist's character class affecting (among other things) whether or not he returns from the titular fantasy world back to present-day Earth, or stays there.
ZanZarah: The Hidden Portal is a subversion: its protagonist Amy is tricked into traveling to another world (which she is supposed to save) but among the first things she finds there is a magical rune that teleports her back to London. Not that she wants to, since her home is a very dull place, constituting one bleak location among hundreds found in the game.
This is the premise of Myst, in which the player stumbles across a mysterious series of worlds after accidentally using a Linking Book. Actually, even if you win the game, you don't get to go home. In the opening of the sequel, Riven, Atrus promises that, if all goes well, he might be able to send the player home. Subverted in Myst III and IV, where the player willfully returns to visit Atrus.
It's implied at the end of Riven that when Atrus drops his D'ni Linking Book into the Star Fissure, he's leaving the player with both a way home and a means to visit him. This was before D'ni turned out to be Earth All Along.
In Brütal Legend, roadie Eddie Riggs winds up in a world based on Heavy Metal album covers after injuring himself and spilling blood on his belt buckle. Turns out that it's a really important belt buckle.
The Avatar of the later games of the Ultima series (from IV onward) is explicitly stated to be a normal human from Earth before he or she is summoned over. According to Word Of God, this is true of the first three games as well.
In Half-Life, Gordon Freeman is trapped in a hellish alien dimension until he can take down the Nihilanth.
In the first Persona game, the party ends up spending a good deal of the game in an alternate version of their city. It eventually becomes a non-subversion: they were actually trapped in Maki's mind (they've just defeated Kandori in the real world when they learn this). Now, Maki herself has been acting strangely since the whole crisis began, and told the group she was from the Alternate Universe they were in- oh,crap.
The expanded backstory of the Mario franchise indicates that Mario and Luigi are actually from Brooklyn, and accidentally ended up in the Mushroom Kingdom. It's unclear, however, whether they can't get home or just choose to stay.
The Hero of Albion ends up trapped on another planet, when losing contact with the factory ship he came with. After he saves the world from the ship's on-board supercomputer that was programmed to destroy it, he essentially traps the crew.
Brad, the player's character in Curse Of Enchantia, is boy from our dimension who has been kidnapped to a fantasy world ruled by an evil witch and now has find a way back.
The plot of The Longest Journey and it's sequel Dreamfall. The main character April Ryan ends up travelling between two worlds, Stark and Arcadia, and ends up as of the second game choosing to live permanently in Arcadia.
In Scaler, Scaler gets trapped in a world filled with Lizard Folk, when escaping from a torture session. We later learn that his father, Leon, is also is trapped there. The rest of game is then spent with Scaler trying to get his claws on a 'Portal Beacon', that can get him and Leon home.
Some of the supplemental material for Touhou states that people quite frequently fall into Gensokyo from our world. Apparently the Great Hakurei Border is not absolutely impermeable.
In Date Warp, Janet and Bradley are trapped in an alternate universe where The American Revolution never happened, and the country is called Atlanta. However, it turns out it's more complicated than that.
You help two people with this problem in The Trail Of Anguish. But it eventually turns out that they may not be the only ones trapped somewhere unknown...
A recurring theme of Super Robot Wars since Alpha Gaiden, since it's the easiest way to put shows that have totally contrasting worlds and backgrounds together.
Webcomics
Invoked in Erfworld, with the summoning of the protagonist, Parson Gotti.
If you count the "Torg Potter" stories as examples, this happens over a dozen times in Sluggy Freelance.
Fur Will Fly: The protagonist is trapped in another world populated by furries.
The main character of Astray³, Emily, transported to another world with almost no explanation as to how. She's not the only one to be magically whisked away like this, either.
Kagerou starts out with this trope, and then does really nasty things to it. It's a long story and involved multiple personality disorder, among other things.
The whole plot of Miamaska, as Amity and Guere are stuck there.
Homestuck: Anybody who plays SBURB will be transported into the Incipisphere. However, the series is more of a Deconstruction of the trope, as the home planet and eventually the universe of the players is destroyed once they leave.
In The Wormworld Saga, Jonas finds a portal to another world on the attick of his grandmother's house. He's Genre Savvy enough to take a thread of yarn with him to prevent the portal from closing behind him. Too bad their cat Wiggins ends up cutting his safety rope while playing with it.
Reman Mythology starts with a curious young woman who finds herself trapped after following a young man with suspiciously supernatural abilities.
A courier in Kukuburi delivers a package only to find a crazy technicolor world.
Winters in Lavelle siblings find that their father's shiny rock leads to a world with more shiny rocks.
Vacationers contend with deadly water in Between Two Worlds while looking for a lost cat.
Sul from Kiss Wood is caught in a fire that destroys his home and blinds him. After a couple of days in the hospital, he loses consciousness and is trapped in a place called Hill. He later learns he's not the only one who has been transported this and left; Ahbon is another person this happened to.
While their trip to Creturia was intentional, the Dimensional Guardians from the web fiction serial Dimension Heroes find themselves trapped in the world until they can find the objects they need to both save the world and return home.
The serial web novel Elcenia starts out with protagonist Rhysel being summoned to the titular Magical Land. Unusual in that Rhysel is from a different Magical Land herself.
This setting is currently the most popular for multifandomJournal Roleplay Games. The community has even coined a phrase for games based around this setting—"spooky jamjar". Which has now come full circle- meet Roleplayedingly. A roleplay where the characters are sent to a new world every week- and every world is an existing LiveJournal roleplay.
The heroes of The Dragon Wars Saga are examples, although it's insinuated they could leave if they knew how and really wanted to do so.
In Trinton Chronicles very first story (Fantasia) all of the characters end up in a portion of the Fairy Realm or something similar.
In King Arthur And The Knights Of Justice, Merlin needs replacements for King Arthur and the Knights of the Round Table, who have been captured by the series' Big Bad. His odd solution is to bring a contemporary American high school football team (whose quarterback happens to be named Arthur King) to Dark Age Europe to become Camelot's new defenders.
The Super Mario Bros. Super Show, where Mario and Luigi are from Brooklyn, but were transported to the Mushroom Kingdom through a warp pipe.
Fry from Futurama gets frozen in 1999 and wakes up 1000 years later. Somewhat subverted, in that even with the robots, aliens, mutants, and new technology, The Future isn't really all that different.
Goliath and the remains of his clan in Gargoyles are trapped in stone for 1000 years, thus arriving in 1994 New York from 994 Scotland.
An episode of Adventure Time had Finn get transported to another world made entirely out of pillows. (The landscape, the wildlife, the people, etc.) He ended up spending the rest of his life there, forming a family and dying of old age, then somehow got sent back to his world a few minutes after his disappearance, with no memory of his time there. It's left ambiguous as to whether or not this actually happened.
