Situations more than monsters stick with me. I had trouble falling asleep for a few days after seeing "The Omega Man" - the monsters were kind of lame, really - purple make-up and dead-looking eyes and not much else. But the story itself - the silent world, and then Norville finding a group of survivors, making a cure from his own blood - at the same time the leader of the survivors gives in to the plague and becomes a monster, and then him dying at the end, leaving hope for the cure to be spread, but he will never know... That whole mix of stuff scarred me more than any single monster ever could.