Quote Originally Posted by Ryllharu
There are a lot more manga of the Gender Bender genre than there are animated series. They tend not to be overly popular. Only three come to mind.

Kashimasi ~girl meets girl~ - Wherein Hazumu, a rather effeminate boy in the first place, gets struck by an alien spacecraft and unfortunately (fortunately for the audience), is only able to be brought back to life as a cute girl. (Alternate title: Kasimasi) AniDB

An older series and probably quite difficult to find now:
Tenshi na Konamaiki: Where Megumi was changed into the "perfect girl" by a demon in a book when he was young, after wishing he would grow up into the "manliest of men." AniDB

And of course, the ubiquitous Ranma 1/2. AniDB

Of course, if you want a wider selection, you can always read manga. There are plenty of series with that sort of thing. List of "Gender Bender" related manga titles
Ah, guess there aren't any more for me to watch then, not really into manga myself :x(I'm totally a visual person)

Macross Frontier is good but a bit short. I "dig" those aircraft transforming mechas like in Vandread and this.

Just finished watching Aishiteru, so good, I hope there will definitely be a 2nd season, kind of feels like it.