No. 2: The Exorcist
The Exorcist - I love this movie. Once in my life I had a very scary incident with a Oiuja board, I've never been able to explain it and I've never touched one since. Luckily, I wasn't possessed by the Devil (that I know of) like Linda Blair was with hers.
This is the classic Good Vs Evil movie. A great story about a Priest who is struggling with his faith as he comes face to face with the Devil. This is one movie I would love to go back in time and watch in the theatre when it was new just to see everyone's reactions.
Pretty tame by today's standards but still a scary story.