Drag Me To Hell is Sam Raimi at his finest, learning plenty from his Evil Dead series in this tale of the Lamia and what happens when you cross little old ladies from the old country.
Let The Right One In is a sweet coming of age story. With a vampire.
The Descent is a great, almost Lovecraftian tale with some great female characters and a chilling, claustrophobic atmosphere. You also really can't go wrong with his earlier werewolf film Dog Soldiers or his post-apocalyptic Doomsday.
Dagon remains one of my favorite retellings of an H.P. Lovecraft story, this one inspired by Shadows Over Innsmouth. Right along with Re-Animator and From Beyond they take some liberties, and some may object to the comedy interjected into these films but few can argue with the overall spirit with which they successfully capture Lovecraft's weird vision.
Dawn of the Dead Whether it's the remake or the original, Dawn of the Dead really serves up some great zombie action for you. The other key zombie films that really vindicate the genre are of course Shaun of the Dead or Zombieland, which alas isn't available out on video yet. 28 Days and 28 Days Later also deserve mention.
Versus gets a special nod for when you absolutely positively need some time-hopping zombie yakuza martial arts action.
Other key Asian horror films that stand head and shoulders above the rest include the original Ju-On, Kairo, Dark Water (NOT the remake), The Eye and Shutter. These all really raised the bar on atmospheric, creepy films that will leave you unsettled. Unfortunately, the industry's gone largely downhill with imitators and not enough time spent on developing the stories. But there was a brief golden era of fine Asian horror with diverse plots and innovation in concepts and excellent technical execution. Hopefully it won't be long before we see a resurgence.