Rosemary's Baby wasn't 'Michael Myers' scary, but it disturbed me and haunted me for quite a while.
May have been cheapened by the goofy sequels, but Child's Play was a pretty terrifying when it came out.
I clearly remember watching a movie when I was around 8 about a guy being chased all over the desert by some sinister semi. That one left a mark on my psyche for a while. Don't remember the name, but it seeing Hitchcock movies later in life often reminded me of it. The fear and anger I felt were very real.
-dave
