Ones I've seen:
1. "9 Songs". Tons of sex (explicit), but legitimate movie.
2. "Baise Moi". Tons of sex (explicit), also legitimate movie.
3. "Romance". Ditto.
4. "Devil in the Flesh". Good explicit blowjob scene. Not the one with the same name from Hollywood of recent years, but the one that came out in the 70's from Italy.
5. "Caligula". Great sex scenes (explicit) but semi-legit movie.
6. "Idiots". Strange movie about some kind of adult handicapped help centre with group sex scenese (explicit).
7. "The Night Porter". Mid 70's film about Nazi Germany. Interesting movie, but the only real sex is between 2 guys.
8. "Pink Flamingos". Famous campy mid-70's film with explicit sex. It is one of the most disgusting movies I've ever seen, made me want to take a long shower after. I hated it, and I never will see it again.
9. "Emmanuelle in America". One of the exploitation films genre. Very very disturbing (the unedited version), impossible to find.
10. "Intimacy". It was a forgettable film, but has explicit sex.
Here are some links with most of the movies out there that have real sex:
http://www.cndb.com/phpBB2/viewtopic.php?t=96&postdays=0&postorder=asc&start=0
http://en.wikipedia.org/wiki/Category:Mainstream_films_with_explicit_sex
http://en.wikipedia.org/wiki/List_of_mainstream_movies_with_unsimulated_sex
http://www.cndb.com/phpBB2/viewtopic.php?t=1019&postdays=0&postorder=asc&start=0
Those links above didn't name my favourite movie, and unfortunately I don't recall the name and I'm not at home right now to find it. But when I do, I'll post the name.