August Underground's Mordum
Beats every film metioned here by about a thousand in terms of sickness.

Although technically Braindead is the goriest movie, as it used the most blood.

It's basically a faux-snuff film, involving a number of gruesome rape, murder, necrophilia scenes. It's pretty hard to find, and I wouldn't particularly recommend it, as it has no story whatsoever and is a pretty crap film.

Saw (I, II, III, IV, V), definetely.
Oh and this movie I watched yesterday - Insanitarium.

Bloody Valentine [:

American Psycho probably.


Christian Bale is such a beast in that movie.