It: Pennywise in the storm drain
These aren't in any order. This scene is #1 because it's the first in my series of the scariest scenes in film history. Why's it scary? It probably depends on how scared you are of clowns. Pennywise the clown shows up in a storm drain, trying to lure a little boy in. Tim Curry's performance and terrifying make-up job as the clown make it what it is. The movie as a whole isn't great, but Tim Curry makes it worth seeing.