I liked Ong Bak and Tom Yum Goong, them Tony Jaa movies
Chingoo(Friend) is a cool Korean gangster flick, prolly one of if not the most popular here
Taegukgi: The Brotherhood of War is a Korean war movie
Choo Gyeok Ja (The Chaser) is about a Korean cop turned pimp
The Good, The Bad, The Weird was a cool movie, it's about colonial times in Manchuria kind of like Korea's version of a western.