So many of these answers are so new. Where's the Exorcist?
One of my personal favorites is Don't Look Now, an early 70's flick by director Nicolas Roeg that still has, to this day, one of cinema's greatest sex scenes. That being said, it's one of the scariest movies I've ever seen.
Another fave is Torso, a 1970's giallo that has my favorite horror scene of all-time.