I am a huge fan of horror films from the 70's and 80's period of cinema. Very few horror films nowadays really don't scare me all that often. The films that have scared me recently and that I found to be good/great was The Exorcism of Emily Rose, Texas Chainsaw Massacre(Remake), Saw, and Final Destination.
Final Destination was scary in sense that it seemed too realistic and it made you think about that extra step into the bathroom, driving on the highway, or simply just hanging out in your room in front of a computer. It was little things in that film that made me paranoid as hell.
The Saw films are really good, I love how they make the audience think and are not full of cheap false scares. The visuals and concepts alone are enough to make the audience feel uncomfortable.
Films like The Omen, The Amityville Horror, The Serpent and the Rainbow, Halloween, Poltergeist, Duel, Black Christmas(Original), The Exorcist, The Hils Have Eyes, Last House on the Left, Misery, Audition, Phantasm, When A Stranger Calls, and etc, etc.... are classic horror films that can never have their atmosphere or the concepts recreated in an original sense.
Horror films then utilized the concept of what you don't see is scarier than what you do see.
t: 
Scared the s**t out of me!
