may be you might be looking for the very classic
Ranma 1/2.
Akane-chan Overdrive - a boy spirit trapped in a girl's body... its a little echi comedy ( same author with Ichigo 100%)
Cinderella Boy - girl pretend to be a boy in a boy band group.
Fushigi Yuugi Genbu Kaiden - theres a star warrior who is a boy can change into a girl.