The best ones that I've seen in the theater this year were:
Bug (its a really good movie, psychologically frightening at times)
The Messengers (again not a very scary movie, and relies on the same old cheap tricks, but I didn't hate it, and the story had its moments)
The Abandoned (Haunted house type of movie, but I really enjoyed the story and the acting. Had some 'scary' moments but nothing truly scary.)
28 Weeks Later - Zombie flick, high action, some good acting, tense story.
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But yes I haven't seen any truly scary movies among 2007 releases.
Though at times 28 Weeks Later had me on edge.
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Among 2006 releases a lot of people seemed to love The Descent. I thought it was ok. They had this whole character setup story which really didn't fit well with the rest of it, and had its inconsistencies. Some people thought the idea of women having the power and strength was original... well they never saw Alien I guess... or several others. Also the whole movie had little scaryness to it once you realize what was going on. Not a bad movie but not great.
I preferred The Cave. It was a supernatural movie, with alien/jaws types of scaryness but I just loved the characters and enjoyed the story.