Bailish at 2010-05-07 09:40:20:
Two horror movies off the top of my head:

Day of the Dead
The Shining
Ryan H. at 2010-05-07 10:26:08:
We can't leave out ROSEMARY'S BABY. Terrific screenplay.
Peter Dwight at 2010-05-07 10:44:56:
Poltergeist is pretty classic from Speilberg.

http://www.dailyscript.com/scripts/Poltergeist.pdf
jeff & at 2010-05-07 11:41:52:
One of the scariest ones I read is Kristy -
Ricardo Cantoral at 2010-05-07 15:35:31:
Maniac Cop 1&2 (Yeah these aren't classics but they are pretty entertaining)

Dressed To Kill
Ricardo Cantoral at 2010-05-07 16:10:37:
I guess Henry: Portrait of a Serial Killer does count as well.
Viewers Like You at 2010-05-07 22:04:24:
i would add Nightmare on Elm Street. both the first ones (the comparison could be fascinating)

and I would nix Zombieland. it isn't really horror. it's a post apoc buddy road comedy with zombies in it.
Nate Winslow at 2010-05-08 09:26:20:
THE MIST.

2005 draft: http://www.sendspace.com/file/6s37pd

And in case anyone likes to see how fantastic scripts get more fantastic, here.

2006 draft: http://www.sendspace.com/file/ewuohz

SILENCE OF THE LAMBS: 1989 draft - http://www.sendspace.com/file/zp32na
1990 draft - http://www.sendspace.com/file/pib0mp

THE THING: http://www.sendspace.com/file/4aia6u

And I'd say you could look at ALIEN as a horror film too:

Dan O'Bannon's draft - http://www.mediafire.com/?ml3xmj3ykug

Hill/Giler draft that Scott has mentioned before (the "haiku" style) - http://www.mediafire.com/?tt2w2oymoin
Ricardo Cantoral at 2010-05-08 09:37:58:
Silence of The Lambs falls into more of the thriller category. Hannibal is more of a horror film though.
Sean at 2010-05-08 09:50:55:
nate, excellent links... would it be too much to ask for more horror script links, please.

many thank yous for the ones already provided.
Nate Winslow at 2010-05-08 09:59:47:
I'd argue you could learn a lot about what makes great horror movies great by looking at things that LAMBS does really, really well. But yeah, not a straight up horror movie.

And no problem Sean! Glad to help out. You looking for something in particular?

@Scott: I have nothing better to do right now, so I'm compiling a running PDF with all of the script recommendation lists we've got so far. Trying to find all the screenplays mentioned and linking them into the PDF. I'll send it to you when this finishes?
Ricardo Cantoral at 2010-05-08 14:00:10:
Yes I do agree Lambs does have some elements of horror in it; Both the scenes with Dr. Lector and Jame Gumb.