i'll second (third?) "valhalla rising" ... too bad the score hasn't really surfaced beyond a track or two.
seconding/thirding/fourthing "irreversible." there's some truly amazing sounds on that disc, but it does get a little too electro-dancy for my liking towards the end... but man, "rectum" is fucking creepy.
"eraserhead," of course ... i'll even add "INLAND EMPIRE." the song selection was decent, but the score and sound design is where the true brilliance really lies.
"a serbian film" -- everyone's gonna think of "that dubstep song" that was used in the trailer, and yeah, it's on there, as well as some other techno-sounding stuff, but it's rough and aggressive enough to not be irritating. the rest of the disc is just cold, atmospheric industrial. great stuff.
"children shouldn't play with dead things" is one of my favorites, despite the fact that all i've ever been able to get is a rip of the sound directly from the film (no soundtrack was ever released) -- but it's all really dark analog synth noise ... really great. rips are floating around online....
shit, there's so many more....