Glad to see others giving props to "The Descent"
and "The Devil's Rejects".
I would have mentioned "28 Days Later"
too, but it totally slipped my mind! I agree it's a really awesome horror movie...not a straight "zombie movie", but very much in the tradition of those, but actually more serious and intense than a lot of them (which tend to have intentional and unintentional camp in them), and I personally liked it better than both versions of "Dawn of the Dead"
I'm not sure what to make of "The Blair Witch Project",
I was totally fooled by the ad campaign when I first went to see it, so I really loved it, but I wonder if I would like it as much watching it again without being under the delusion that it's a true story.