Do you mean gender stereotypes or stereotypes of a person's sexual orientation? To be honest you can go into great depths with these and research the historical roots of them, you'll notice that ones concerning homosexuality are often offensive! (I wonder why? *sigh*)
Gay man: camp, over the top and wears lots of brightly coloured clothes, hangs around with women a lot and are usually very slim.
Lesbian: man-hating, hard, butch
Bi (girls anyway): often get called sluts- like they're out to sleep with anything that moves.
I don't really know about bi boys though- anyone help?
These are the stereotypes though! There may be some root in truth but they're often exaggerated. I don't know any man-hating butch lesbians for example, the ones I know are pretty keen on being normal- like any other girl you'd meet.