I've always felt that Red Heat was an under-appreciated Schwarzenegger film. Of course, Walter Hill knows a thing or two about great action too.

I love just about all the ones mentioned here so far but don't believe anyone has yet mentioned my top three:

1) Seven Samurai
2) Hard Boiled (1992)
3) The Wild Bunch

Other Greats: The Road Warrior, the HK films of Bruce Lee & Jackie Chan & Sammo Hung & Jet Li, Gone in Sixty Seconds (the original) & The Junkman, John Woo's Better Tomorrow 1 & 2 and Bullet in the Head and his unreleased cut of Hard Target, Point Break...