Well...that King guy again...
I was always impressed with the original Salem's lot. The TV version from the 70's with the Starsky and Hutch guy. Very creepy visual when kids start floating outside the 2nd story window. The impressive part is that this was a TV movie with virtually no blood whatsoever.
The original Amityville Horror was good.
I kinda agree with @ohanacreek in that Aliens, Vampires, and killer Ewoks (aka Gremlins) aren't really "horror" to me. Aliens, for example, is one of my all time favs...but i can't say it was scary. The paranormal stuff...well, i think we can all agree that there are forces we don't see or understand. Having you as the target...thats scary!!!
@Plumber32 after you posted Pet Sematary thing, i must confess i had forgotten most of the differences between the movie and the book, so i did some research and it brought back some of the truly eerie stuff that was in that book, and unfortunately, the movie omits lots of this. King himself has said it was the scariest book he has ever written...to the point that he didn't want to finish it. I thought the movie was good...but the book is levels above, as they usually are.