The Girl Next Door - not the fun porn-star one http://www.imdb.com/title/tt0830558/ That movie messed me up. A this kind of thing does happen, which is why it hits you so hard.
Pan's Labyrinth is a really dark fairytale, set against the backdrop of the spanish civil war: http://www.imdb.com/title/tt0457430/
harsh times is definitely dark/disturbing. days after the movie is over i was still thinking about it. donnie darko gets a nod from me, very strange. event horizon creeped me out for years as a young kid/teenager.
Agree with Kids and Deer Hunter. You should also take a look at a foreign film called Irreversible, with Monica Belluci. Quite disturbing.
For dark, disturbing and plausible, I'd have to go with 8mm. I've seen some messed up movies, but the stuff in 8mm could and probably does happen.
Dark has nothing to do with scary, although it could be scary in a disturbing way. Dark is more the true evil and wicked side of things - abominable.
I just saw The Black Swan. It's pretty dark. Same director as Requiem for a Dream. I also found The Cable Guy to be dark.
I agree, the Road was one of the most depressing, dark movies. The grey skies the entire time, the house with the basement scene.......
The Road, Winter's Bone were both pretty dark and depressing in a "it could happen" and "that's how it is" way. I thought both were done really well though. Saw a Brit movie called Eden Lake(?) I think was the name. A couple that goes out to a lake and gets terrorized by shitty kids the entire time. No happy ending, sort of an, "that could happen" type movie. I see alot of bummer movies, my girlfriend loves them. Eh.
Clockwork Orange...The dudes in the the white jumpsuits and orange hair still are locked in my head since...oh about 12 yrs old...it warped me badly, man. Saw a documentary on it and the writers producers were some f*cked up dudes. I will NEVER forget the effect that The Exorcist had on me. I think as a young lad it was the first real time I contemplated the realm of real evil and the Debil. When that bitch's head spun around and she puked green bile onto the preacher...whew! When good (God and faith) confronted with Evil (Devil/sin) and Good won, but not without a helluva battle, I realized I needed to get my shit in a pile and get serious about true faith in God. Now, I'm headed to The Dungeon to vent... Edit: I don't know why, but that movie with Dennis Hopper and the "dark, evil man-less" diesel 18 wheeler chasing him just chilled me...