1. Liar Liar
Jim Carrey is a slimy lawyer who lies a lot, and puts his career before his family — until his son makes a birthday wish that his father should be unable to lie for 24 hours. This leads to lots and lots of scenes of Jim Carrey doing that disturbing rubber-faced, dislocated-jaw thing he used to do all the time, while making weird "I'm trying to lie" noises. (See the helpful clip reel.) Eventually, he figures out how to use the truth to manipulate people, and all is well.
The important lesson: When Jim Carrey is doing that broken-face ululation, it doesn't really matter if he's telling the truth or not.

2. What Women Want
Mel Gibson is a sexist dickwad, who suddenly finds Helen Hunt being promoted over him — and he has to learn to sell women's products, because women are consumers and stuff. So he electrocutes himself while wearing pantyhose, and now suddenly he can hear women's thoughts. All women's thoughts. He uses this power to steal Helen Hunt's ideas and to become a marketing dynamo — but eventually becomes sort of sensitive and stops this one chick from killing herself.
The important lesson: Men should listen to what women have to say. Otherwise, men will never be able to steal their ideas properly.

3. A whole slew of Adam Sandler films, including The Hot Chick
Probably the most heinous example of an Adam Sandler-produced film with a painfully high-concept magical setup is The Hot Chick, in which Rob Schneider swaps bodies with... wait for it... a hot chick. And she learns that it would be a lot less fun to be in the body of Rob Schneider, I guess. Sandler also stars in Bedtime Stories, in which some kids' bedtime stories shape Sandler's future. And Click, in which Sandler gets a magical remote control that lets him fast-forward through the unpleasant parts of life. Etc. etc.
The important lesson: Mostly, it's "be thankful for what you've got." And "people will actually pay real money to watch Rob Schneider trim his nose hairs and learn how to pee standing up."

4. 13 Going on 30
Tween Jenna wishes she could be "thirty, flirty and thriving" — and then suddenly, she is. (Relevant scene is in the video above, at about 2:45.) She finds herself running a big-time fashion magazine, and in the tradition of Big, Vice Versa, Freaky Friday and other similar comedies, she's a fish out of water. And she soon realizes that the grown-up version of Jenna is mean, manipulative, backstabbing and friendless — because she's the popular girl she always wished she could be. And the boy she always liked is marrying someone else.
The important lesson: Being a grown-up sucks. Or maybe, you shouldn't be a fake stuck-up person. Actually, I'm pretty sure it's that being a grown-up sucks.

5. Shallow Hal
Hal (Jack Black) is a jerk who only sees the superficial beauty of women — until he's stuck in an elevator with Tony Robbins (playing himself!) who hypnotizes him into seeing only the inner beauty of women, not the outer beauty. (This appears to go way beyond hypnosis, since Hal gains an unerring sense for which women are inwardly beautiful, almost as if he were some kind of spiritual detector. Even when he's meeting a woman for the first time, he instantly can tell whether she's inwardly beautiful, and sees her accordingly.) Soon, Hal falls for the boss' daughter, who looks like Gwyneth Paltrow to him, but actually looks like Gwyneth Paltrow in a fat suit. Including lots of sight gags where the skinny Paltrow is making Hal's boat tip over and stuff. Ha ha ha ugh.
The important lesson: You shouldn't judge people by appearances and stuff. And we should all be glad the horrible "fat suit" trend is over, for now at least.

6. Bruce Almighty
Jim Carrey is Bruce, a TV news reporter who can't seem to catch a break — until he complains to God, who grants Bruce all of His powers. Soon, Bruce is abusing the hell out of his power, while also totally failing to cope with the avalanche of prayers sent to him. (At one point, he tries saying "Yes" to all prayers, with the awful results that a five-year-old could have predicted.) He enlarges Jennifer Aniston's breasts, and tries to make her love him by waving his hands and droning, "Love meeeee..."
The important lesson: God moves in mysterious ways, and power corrupts, and you should be yourself, and be thankful for what you have. Oh, and Jim Carrey should never try to lip-sync.

7. Tooth Fairy
Dwayne "The Rock" Johnson is a mean hockey player who breaks people's teeth, hence the name "the tooth fairy." The Rock is such a "dream crusher," the fairy bureaucracy forces him to become an actual tooth fairy for a few weeks. He gains the power of flight, shrinkage, invisibility — and amnesia dust, which basically lets him inflict severe brain damage on people. Cue lots of scenes of The Rock in fairy wings, attempting to take people's teeth stealthily. Eventually, he learns to be slightly less of a dick, and even makes it up to one little girl whom he told the tooth fairy wasn't real. "I'm not talking about the hockey tooth fairy," he explains, helpfully.
The important lesson: You shouldn't crush people's dreams. Or maybe, sneaking into kids' bedrooms and sprinkling them with amnesia dust is awesome.

8. Ghost Dad
Bill Cosby is a businessman who never has time for his family — until one day he gets into a cab driven by a Satanist, who's also an unsafe driver. Cosby decides to impersonate Satan, as a way of improving the cabbie's driving, but this leads to a car accident in which Cosby apparently dies. But his ghost hangs around, and people can see him but not hear him. So the ghost decides to keep holding down his job and looking after his family, only to have wacky hijinks ensue.
The important lesson: Uh, don't pretend to be Satan in a taxi? Actually, the real moral is that you should always make time for your family, because it's too easy for a mute ghost to get carried away with career stuff. Really.

9. Switch
Blake Edwards broke his awesomeness streak, which had included 10, the Pink Panther films, Breakfast at Tiffany's and Victor/Victoria, with this dreadful movie. In it, a womanizer gets murdered in a hot tub by three of his ex-girlfriends, and God gives him a chance to redeem himself by coming back to life — as a woman. Now embodied by Ellen Barkin, Steve learns about sexism n stuff, uttering classic lines like "He's about as sensitive to a woman's needs as Jack the Ripper!" and "I'm sick and tired of being treated like a piece of meat!"
The important lesson: Being a woman "has its advantages." And Ellen Barkin acting macho is kind of hot.

10. Just My Luck
Lindsay Lohan is the luckiest person in the world, who always has everything her own way. Until she kisses Chris Pine, and they trade — Pine gets Lohan's good luck, and she gets his bad luck. (Please, no comments about how this happened in real life, too.) Cue lots of scenes of Lohan acting like a total idiot, and wreaking destruction, because she's not used to things not falling into her lap.
The important lesson: Kissing is bad. No, wait. I mean, it's better to wish good luck on others than on yourself.

Source: Box Office Mojo has great lists of God comedies, body-switching comedies, and "what if" comedies