The best kind of movies are the ones when you can never tell who the good guys are and who the bad guys are; that moral complexity of who to root for. Usually villains are so much more colorful and cool that it's just so much easier to want to see them pull of the heist and get away into the sunset, than see them end up behind bars for the next thirty years. Then again, sometimes it's just as cool to watch them get riddled by enough ammo to make them dance like MC Hammer.
That's why undercover cop flicks are so much fun to watch: you never know who you really want to see win at the end. You spend the entire movie digging your nails into the palm of your hand because you know any second that tattooed gangster is going to find out his new best friend who saved his life earlier in the film is actually carrying a badge.
And now that Sleeping Dogs' release is finally upon us, we take a look at the five best undercover cop movies you should be marathon-watching right now.