I’m not talking transexuals. I’m talking about movies where the character may say, "I wonder what it would be like to be (the opposite gender than I am)’, or “I wish I was a (the opposite gender) because they have it made” type movies.
I can think of one:
Willy/Milly (AKA “Something Special”)
I’m sure there’s been others.
Tilda Swinton in Orlando.
Switch with Ellen Barkin and Jimmy Smits (although the lead character didn’t really “ask” for the gender change).
I didn’t see that one. Didn’t he stay a she?
(Much as I hate to say it): The Hot Chick.
A Florida Enchantment from 1914 is arguably the genesis of the genre.
Switch is basically a remake of Goodbye Charlie.
And from TV there was Turnabout.
It’s a bit of a stretch, but Lily Tomlin inhabits Steve Martin’s body in All of Me.
One of my all time favorites…
Some Like It Hot
Happened on the TV show Boy Meets World
There are a bunch of Shakespeare plays that would qualify if they’ve been made into movies.
How about every single Ranma 1/2 movie? 
Some Like It Hot wouldn’t qualify, as no one changed from one sex to the other. I’m not familiar with Boy Meets World but I would be amazed if a show aimed at a teen audience would include magical sex-changes. As for Shakespeare’s plays, there were instances where males masqueraded as females and vice-versa but I’m not aware of any true sex-switches (but I’m hardly a Shakespeare scholar).
In Deathstalker an evil wizard’s male minion is transformed into a female minion so that he may easily approach and kill Deathstalker. He transforms back when Deathstalker kills her/him during the assassination attempt.
In Monty Python and the Holy Grail, John Cleese was apparently transformed into a newt by a witch. Now, it may have been a female newt – that is not made clear in the movie. And he changes back when he gets better, also apparently.
You people are reachin’. Cross-dressing (for practical reasoins), as in Some Like it Hot, ain’t gender change. If it were, we could make this a long list. There’s no real gender change in Shakespeare, either, although there’s a lot boys dressing as girls and vice-versa.
And putting in Monty Python and the Holty Grail’s newt is really stretching it.
Switch and Where’s Charlie are tjhe ones that came to mind. In addition to the ones listed above, there’s the anime Rei Rei, where a guy becomes a girl temporarily (with the aid of the moon goddess) to get revenge.
Gender-switching used to be common in comics and on kid’s shows (like the adaptation of “The Land of Oz” that I thought was a special in the early 1960s, but have been told on this Board was an episode of The Shirley Temple Show. It was, in turn, a direct adaptation of the gender-switching story by L. Frank Baum) I think someone got worried about the sexual implications, because it disappeared for a few decades. But I notice that episodes of new cartoons – Jimmy Neutron and Fairly Oddparents, both on Nickelodeon, have used it recently.
There was a bit related to this at the end of “Don’t Tempt Me” (Penelope Cruz et al as angels/devils fighting for the soul of a boxer. Kind of “Dogma”-ish), which I think might be video-only here in the states. Spoiler avoidance prevents me from saying more.
Though frankly, that particular bit lowered the movie a lot in my estimation.
I seem to remember an episode of The X-Files invovling Amish people who could change gender at will. Don’t remember much else about it, but here’s a review I turned up with a Google search
http://www.munchkyn.com/xf-rvws/genderbender.html
I caught this movie on HBO? Cinemax? a few years ago. It’s about a girl who makes a model of her ideal man in a virtual reality booth and then, due to a technical glitch, suddenly finds herself in the body of the guy she just created.
Well, given that Switch has him reincarnated as a woman, then I suppose Dead Again would count, too.
I suppose Prelude to a Kiss might also qualify.
If the BMW episode is the one I’m thinking of, it doesn’t count. The character merely posed as a female in order to write an article for a school paper.
In both Switch and Prelude to a Kiss, I don’t believe the characters chose to change genders. They were reincarnated as the opposite gender.
I’ve never seen The Hot Chick (and you can’t make me, nyah!) so I don’t know the circumstances of the switch.