I believe thats called a quadrilogy these days
If you've seen the extended version of the Wicker Man its slightly less disturbing than the theatrical purely because it expands on the motives of the islanders a bit more and adds another song or two, but Christopher Lee says its the best version so I go along with him. An American Werewolf in London is another of my favourites, but in a just as funny as scary kind of way. I cant think of any film thats really scared me in recent memory, with the exception of Ring which freaked me out a bit. Everything seems to be new takes on the old genre such as The Others or just splatter nonsense.