I would second Monkey Boy's pick of "The Descent". I saw this movie about six months ago and I gotta say, it was freaking scary. It's rare for me to get scared watching a movie, but this movie was just tense from about twenty minutes in to the end. And just like "The Innocents", this movie had different meanings and a ton of symbolism.

"SuperSize Me"

It scared the McShit out me to see what I had been doing myself all these McYears.

I also believe that "The Descent" was very good. It makes for a scarier film if I believe that such a thing could happen/exist.