Didn't catch this thread first time around because I wasn't here, but just took a look at the linked list. I spit on it. *ptui*
Looking back at the first page, my thoughts:
Alien -- a monster lurking in the dark, killing unsuspecting victims in a sprawling yet confined location with all manner of nooks and crannies to hide in: definitely horror. The sequels, not at all.
Jaws -- an aquaphobic sheriff sets to sea to capture a great white shark. Thriller? Yes. Horror? No.
IMO. As for my top ten list:
10. Night of the Living Dead
9. Day of the Dead
7. Return of the Living Dead
6. Texas Chainsaw Massacre
5. Evil Dead 1 & 2 (I rate them even)
4. The Thing '82
3. The Exorcist
1. Dawn of the Dead
The bottom five could change depending on my mood, but the top five are pretty much set in stone.