4. The Exorcist (1973)
"The scariest film of all time" as its posters proclaimed, and I have to say I agree. In terms of absolute horror, The Exorcist can't be topped. It's utter demonetization of everything that's holy not only makes it horrifying but also controversial. There are no two things that a horror film needs to be more than horrifying and controversial and The Exorcist has these in spades. It spawned every religious themed horror film that followed and has never been more influential than right now with The Last Exorcism Part 2 set for release very soon and The Rite taking the #1 box office spot in early January of 2012. There are too many iconic scenes of The Exorcist to mention in this one post alone but who can ever forget the spinning head of a possessed Regan MacNeal, the very unholy act she performs with a holy object (you know the one I'm talking about), the vomit scene or the "spider walk" down the steps?