Mind, I was a kid when I saw it. Even the book cover scares me.

um...the murderous clown? Actually the look of Pennywise was scary but what actually haunted me and still effects me at night is the whole plumbing issue. I remember a scene where a little girl is in the bathroom and suddenly her sink starts gurgling...(gargling?) and Pennywise talks to her...from the sink! To this day I get freaked out going to the bathroom at night...or even during the day. Especially if the sink is clogged!