Green Room. I only heard about this because Patrick Stewart is in it as the leader of a bunch of neo-Nazis. Yes, you read that correctly.
It's a nasty little thriller that I quite enjoyed. For some reason it's billed as a horror movie, but it's really not.
Without spoiling anything it's about a punk band stuck performing for a bunch of skinheads who get in over their heads when one of them sees something they shouldn't. I recommend it.