I think The Exorcist has to have top honors in my book re scariest.
When the first Evil Dead came out and I watched it on video, it really creeped me out LOL.
Oh and the FIRST Trilogy of Terror (with Karen Black), definitely can't count that out! The second one they made a few years ago was OK, but just not the same as the first one.
Also there was this one movie I saw a looong time ago, haven't seen it in ages, it was just a TV movie, called Don't Be Afraid Of The Dark. Anyone see that? It was an older movie, probably made in the late 70's. People move into a house, and the fireplace is all bricked in, so they un-brick it (of course) and end up freeing these little monsters that were in it LOL.