28 Days Later? I thought that was a sequel to Sandra Bullocks movie.
Anyway, there are some good scary films listed so far. You have to see the original versions of The Eye, Ringu, and The Grudge. The American ones, haven't seen what they did to The Eye, but they just aren't as good.
One of the creepiest movies I've seen is Session 9.
The Hills Have Eyes is also scary and gory.
Pink Flamingos is scary too...but on a whole other level.
I'm more of a fan of cheesy, B-movies myself. If you want that, I highly recommend: Dr. Chopper, Andre the Butcher, and Dead and Breakfast (which is actually really good!). The first 2 are supposed to be scary, but are just incredibly bad.