I'm a teen horror nut, so I've seen almost all of these films. Horror’s probably my favorite genre, so I can't say (without bias) how many of these are essential. I can say that all of them are very good.
Henry: Portrait of a Serial Killer is one of the more important slasher films ever made. It holds up pretty well, even though if you've seen a David Fincher film, you'll feel some moments of déjà vu.
Near Dark is the best vampire film of the 80s (Fright Night is a close second. Sorry, I can't muster up much love for Lost Boys. It's got a great cast and one of the best bar fights in the history of cinema. Too bad the 3rd Act sucks.)
Even though I love it, The Hitcher should be seen by Ripoll around the time the remake hits theaters. Hauer is great as usual; the diner scene is fantastic and has been aped too many times.
Ripoll, have you seen any Argento films? Suspiria, while one of Argento's better made films, is not a very good introduction to his filmography. It's notorious for dividing audiences. I'd try Deep Red first.
Zombi 2 is a bit overrated. I've never seen a very good transfer of it, but the 3rd Act is pretty fantastic. It's also got the shark scene.
I haven't seen the original House on Haunted Hill in 8 years. I remember loving it, but then again, I was 9 (I loved Creepshow back then too. Now? Not so much.)
Re-Animator is the Holy Grail amongst this collection of films. It shows why Stuart Gordon and Jeffrey Combs are so amazing. It also has some of the best FX of the 80s.
I'm not a huge Clive Barker fan. I don't think Hellraiser is too hot, though it's probably the best Barker film. Just stay away from Candyman, even Tony Todd's valiant performance can’t save that trash.
Martin is by no means a classic, though it's one of the better off-beat horror films. Haven't seen this one in ages, might wanna give it a rent soon.
I've never seen Black Sunday. Hell, I haven't seen much Bava, and I haven't exactly seen as much Argento/Fulci as I'd have liked. I think I might just dedicate this Halloween to catching up on all the Italian horror films I haven’t seen/want to see again.