INDIE SEX is a good doc series about the history of sex in cinema that has been running on the Independent Film Channel. It's pretty graphic, and not for everyone. My only problem is that they tend to lump all types of sex scenes together, from erotic and comic scenes, to rape and incest. There are definitely some unnecessarily explicit scenes in some films referred to in the documentary that might have been more effective if done differently, yet the film defends them.
Nonetheless, it's worth viewing for students of film.