PedroSteckecilo said:
Ichi the Killer is easily the single most violent film I've ever seen but the first Dead or Alive film (not based off the videogame, the strange Takashi Miike Actioners) is also pretty freaking violent.
Oh yeah, and can't forget Machine Girl, another Japanese one best described as super violent.
Mega kudos for knowing of The Machine Girl, I love that film so much but it's only really violent in a sort of live action itchy and scratchy way.
I really need to see some Takashi Miike movies, I've been after Dead Or Alive and Ichi the Killer for ages. For me the most violent film I've seen is probably Cannibal Holocaust, that's the only really ultraviolent film I've seen, although the bottling scene in Pans Labyrinth is brutal, particularly if you watch it right after the choreographed bloodshed of 300.
EDIT: looking at films other people have mentioned holy crap am I desensitized, I've seen Evil Dead, Dead Alive, Hellraiser, (the original) Hills Have Eyes, Planet Terror and A Clockwork Orange and didn't think they were that violent.