Save the Green Planet and Thirst are both pretty interesting Korean movies. Wing Chun is an amusing martial arts movie, probably one of my all time favorite movies. Not sure if it would count as being underrated considering it won an Academy award for best foreign film, but it may not be very known since it is foreign, so I'll mention Tsotsi. Also awarded but possibly not well known: In The Mood For Love.
...can't really think of anything else off the top of my head that would be underrated and that hasn't already been mentioned. =P