Bureau 13. Just for the Foglio artwork in a horror RPG.
No? How about Beyond the Supernatural? Chill? At some point I should write a blog post about me and horror RPG's and how they never, ever seem to work out. I'm too much of a clown, my group is too relaxed, I'm gaming with five teenagers, and frankly horror is too easy to slip from inspiring fear and terror in your imaginary character's situation to being a "kill the monster" scenario.
Call of Cthulhu gets close to this. You don't fight the horrors of the Lovecraftian mythos. My EOW game system is also pretty good for horror games, because it is so damned easy to die in it (and once you do, you're kind of stuck for the rest of the day-long gaming session) so you're less likely to say, "I just draw my pistol and start firing."
But I have really, really struggled with the horror genre to the point where I can not honestly say I've had a good enough experience as player or GM to have a favorite. So this is my "pass" day of the blog-a-thon, I guess.