TOD: ROSEMARY'S BABY would have to be my favorite, and it's also a classic in the best sense of the word: classy production, vivid performances, superior direction.
THE HOUSE ON HAUNTED HILL scared the beejesus out of me back in the day. The theater where I saw it didn't have the skeleton that was supposed to fly over our heads, but I didn't need it. The movie still scared me silly. That one famous moment can still give me the creeps even though I know it's coming.