There are a quite a few mangas that involve girls liking to dress up as guys, forced to dress up as guys, etc. and also mangas that have guys that are mistaken for girls or dress up as girls.
Personally I really have fun reading the mangas where girls dress up as guys to get into an all-boy's school.
For example: Power! ~ Girl Got Game, Cinderella Boy, etc.
If there was a genderbender genre, it would be way easier to find the mangas that involve girls looking like guys and guys looking like girls (crossdressing sounds a bit too direct, genderbender is cooler ).