These are the formative films in your creation as a horror junkie. No matter how often they get re-released, you MUST have (or are at least severely tempted) to have them in the best edition possible.
Mine are (in stream of consciousness order):
2) The Fog
4) Halloween III: Season of the Witch
5) The Howling
6) An American Werewolf in London
8) The Beast Within
9) Horror Express
10) Time Walker
11) Salem's Lot
12) The Boogens
13) Creature From The Black Lagoon
14) Shock Waves
15) The Children
17) The Incredible Melting Man
18) The Monster Club
19) Friday the 13th Part 3 in 3D
20) The Shining
Actually that's it. I think at that point I'm basically padding out the list. As you can see I'm a big Carpenter fan. He takes up a full quarter of the list.
I'll leave two slots open just in case somebody else mentions a film that's name escape me at the moment.