The basis of P. G. Wodehouse's novel Laughing Gas, in which Reginald, third Earl of Havershot, and Joel Cooley, child film star and the Idol of American Motherhood swap bodies while under sedation at the dentist. Reggie's narration makes clear that this was already a well-worn trope by the 1930s, as Reggie is familiar with the idea and muses about how in fiction, the people who fall victim to this are never believed.
Older Than Radio: Used in F. Anstey's 1882 novel Vice Versa to swap a father and son. This may have inspired Mary Rodger's 1972 novel.
In Marghanita Laski's novel The Victorian Chaise Longue, a modern woman buys a Victorian couch at a bargain price because it has an old dried bloodstain that can't be removed. Falling asleep on the couch, she wakens on the same couch in Victorian times, inhabiting the body of the couch's original owner. The couch is now new and unstained, and the woman suspects (correctly) that her impending death will cause the bloodstain.
Happened in the Doctor WhoExpanded Universe novel Half Life, although with a bit of a Personality Swap element — despite swapping all their habits, personality traits, and their memories, they retained their basic selves, and afterward remembered what it was like to have the other person's mind. Apparently, it's really fun to be the Doctor, not so much the companion he swapped with. There's a very touching scene after they've switched back where the Doctor actually cries — which is a big deal for him — because he hadn't realized before just how much hell he puts his companions through.
Happens to two of the protagonists of Esther Friesner's Harpy High; since one of them has a physically abusive father, the other one acquires a little more understanding than he wanted.
In Diana Wynne Jones's book The Ogre Downstairs, a mystical chemistry set leads (among other things) to two kids in a recently blended family switching bodies for a day. This is the first step towards the two sets of children actually getting along. The swap is discovered after two not himself situations.
Mary Rodgers' 1972 novel Freaky Friday, on which the film adaptations are based and for which the trope is directly or indirectly named, switched a mother and a daughter.
The sequel, Summer Switch, swaps the other members of that family, the father Bill and the son Ben (a.k.a. Ape Face).
Anton and Olga switch minds in The Night Watch as part of a plan to draw out a plot by the Day Watch. The scene also averts No Periods, Period by having Olga tell Anton that he's lucky this isn't happening a few weeks later, or she'd have to instruct him on the use of tampons. In a Deadpan Snarker manner, Anton replies that he knows what needs to be done: he needs to pour some blue liquid on the tampon and the squeeze it in his fist, like all the commercials show. Anton's reply is absent in the English translation (possibly because women use pads now).
The film version has this swap occurring in the second movie, Day Watch.
Occurs in Paul Collin's Jelindel Chronicles. Zimak tricks Daretor into swapping bodies, after saving him from a prince who was trying to do just the same. Daretor by this point is getting truly frustrated, as already his sword skills were magically stripped from him, and now he had to deal with being in a much weaker body after being a tank. And in these books, changes tend to be permanent.
In The Mirror, by Marlys Millhiser, the titular family heirloom swaps Brandy McCabe (in 1900) and granddaughter Shay Garrett (in 1978) on the eve of each woman's wedding.
In the second book of the Love Hina light novel series, Motoko and Kitsune are switched by Motoko's older sister. (Suu and Shinobu are also switched, albeit briefly).
Happens to the male heroes of Riddle of the Seven Realms by Lyndon Hardy, as a side effect of a time/space-warping magical weapon. Unusual in that it's done neither for social commentary nor comedy; rather, it gives the djinn hero a chance to experience life as a human, and vice versa.
In the Goosebumps book "Why I'm Afraid of Bees", Gary, the main character, stumble upon a service that switches you with whoever you want. However, he accidentally ends up in the body of a bee. Horror ensues.
The entire premise of the kids' series Katie Kazoo Switcheroo is this trope. She switches bodies with other characters partway through each story, thanks to a magic wind.
The 1931 novel Turnabout by Thorne Smith (see above for the 1940 film adaptation), in which suburban couple Sally and Tim Willows have their bodies switched by the statue of a minor deity in their house who becomes fed up with their constant bickering. Sally now has to take over her husband's job in an advertising agency and on a drunken night manages to impregnate Tim, who in chapter XVIII "was delivered of his child and became by virtue of the achievement the first male mother on record."
Magic: The Gathering: In Agents of Artifice, Jace Beleren accidentally induces a flip between himself and his friend Kallist. The swap is so thorough that neither party even realizes anything has changed—each goes about his own business as usual, believing himself to be the other.
In Beatrice Gormley's Fifth Grade Magic protagonist Gretchen and her rival Amy spent most of a day in each other's bodies as the result of an overly-enthusiastic Fairy Godmother wannabe.
In Parker Pyne Investigates, an obscure Agatha Christie series, Mr. Parker Pyne's job is to make people happy. In "The Case of the Rich Woman", a rich widow named Abner Rymer comes to Parker Pyne requesting help with her boredom since she has buckets of money and nothing enjoyable to do with it. He hires a doctor who manages to switch her body with an Identical Stranger farmgirl named Hannah. Things seem to go wrong almost immediately when Abner reads a newspaper suggesting that Hannah was locked in a mental institution for claiming she wasn't Abner. It turns out to be a subversion. "Hannah" never existed and the newspaper was fake. This was all part of a plan to give Abner happiness. It works.
The premise of the Todd Strasser book Help! I'm Trapped... in My Teacher's Body, as well as most, but not all, of its sequels.
Near the end of book six of Captain Underpants, Mr. Krupp and Melvin Sneedly accidentally swap bodies. Getting them to swap back takes up much of the plot of book seven.
Gets a Darker and Edgier treatment in We Can't Rewind, which seriously examines some of the unsettling and far-reaching sexual implications parent-and-child swaps as in the original Freaky Friday story might have if the parents in question were married and the swaps couldn't be reversed.
One of several Gamebooks based on Club Penguin (the "Pick Your Path" books), "The Great Puffle Switch", is based around the viewpoint character (a penguin, obviously) swapping bodies with their pet Puffle (i.e. small fuzzy limbless creatures kept as pets on Club Penguin for the uninformed) after a lightning related mishap at the Night Club.
In The Shape Changer, Lafayette O'Leary finds himself swapping bodies with a series of strange people for reasons he doesn't entirely understand. It starts with a local thief named Zorro, but soon after, he finds himself swapping with people from other worlds. It's an unusual variant where the minds stay where they were, and the bodies change places.
In kid's picture book A Twisted Tale by Carolyn Fisher, the animals that live on a farm belonging to the Tarbell family end up apparently switched around this way after getting sucked up by a tornado, resulting in the cow crowing every morning while the duck moos, the cat barking at and chasing the screeching dog, and the oinking chickens wallowing in mud while the quacking pig wades in the water and wrinkles up like a prune. After numerous failed attempts to return the animals to normal, the farmer's daughter solves the problem by going to the fair and loading up herself and the animals onto a tornado-themed roller coaster. The ride returns the animals to normal, but with the side-effect of turning the daughter into a wind-swept, noodle-limbed nut.
Fear Street has Switched, where a depressed girl named Nicole is offered to switch bodies with her friend Lucy. Subverted when it turns out that this was all in her mind, as Lucy died a while ago and Nicole couldn't cope with it. It's sister series, Ghosts of Fear Street had Body Switchers from Outer Space, where a klutzy boy named Will switches with the popular kid, who turns out to be an alien.