Just a short list:
Kiss Kiss, Bang Bang: criminally underrated. Both Downey Jr and Kilmer are terrific. Very entertaining.
Dead Alive: One of Peter Jackson's first movies. Very very very gory and over-the-top violent. Great movie to watch with friends and a couple of drinks.
[REC]: Spanish horror film. Very well made. Was remade in America as "Quarantine" but the original is better. Apparently the sequel is pretty bad though.
Memento: I thought this was a pretty well-known movie, but I've been shocked to find a lot of my friends haven't seen it or even heard of it. One of Christopher Nolan's first, and an excellent mind-bender of a film.
The Running Man: Not really a good movie at all, but a fun, ridiculous 80s Schwarzeneggar flick. This and Commando seem to have been forgotten over the years, which is a shame.
Jacob's Ladder: I'm not giving anything away, just watch it.