[rec] (which was remade as Quarantine and released earlier this month) and Inside.
Inside especially, though it is not for the faint of heart.......or pregnant women. Not much phases me anymore since horror has been a genre I've loved since I first saw Child's Play 2 when I was in grade three. But when I saw Inside earlier this year I was uncomfortable just going upstairs to get a drink afterward. Inside is a French film, if you like gore (and I don't mean Evil Dead gore, I mean serious, painful looking, brutal gore) and want something a bit more adult in nature than the typical horror film, check it out.
I haven't seen Quarantine, but the last 15 minutes or so of [rec] is one of the best examples of rising tension I've ever seen in a film. You feel just as trapped as the characters. Great stuff.