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.
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 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: The Case of the Rich Woman, an an obscure Agatha Christie series. Pyne's job is to make people happy. A rich widow named Abner Rymer comes to 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.