We watched
Infernal Affairs, which was regrettably dubbed rather than subtitled, but pretty good nonetheless. I had heard really good things, and was slightly disappoitned, but the plot idea is very compelling -- Hong Kong underworld and police each have a "mole" planted on the other side, and they are both essentially racing to figure out who is the other side's mole first, to save themselves.
From the imdb link, I see that this is on its way to being remade/butchered by Hollywood... but I am buoyed by the names Scorcese, DiCaprio, and Damon being attached, so perhaps there's hope for this one to turn out well.
Anyway, the original gets 7/10 for me... might have gone a tick higher with subtitles.