I've been a horror fan from a very young age, I've watched all the slasher movies, ghost movies, zombie movies, you name it. But the one that got me when I was young (and you're probably going to laugh) was Robocop. Not the whole movie, just the scene near the end where the bad guy gets hit by a car and then into (atomic waste, acid, ???) His skin is all melting off and he's walking around yelling "help me, help me" then he gets hit by a car and disinigrates.
I remember being in the shower days later and just knowing that that melting freak was outside the curtain. Scared the heck out of me for weeks!