The Departed
Fantastic movie from start to finish. A who's who list of modern day famous actor are in it as well. The ending is a classic and the first time you experience the ending you can't help but go, "Whoa! I didn't see that coming." I have been to Boston a couple of times and love the fact that it takes place there. Will be a classic police movie forever.
Bad Lieutenant
The original one with Harvey Keitel, not the remake with Nicolas Cage. The movie is dark and dirty and honestly makes your skin crawl with how shady of a cop he is. Terrible image for the police profession, but from a film/acting perspective it is great. Basically if you want a movie on how not be a cop and how to end up in prison as a cop, watch Bad Lieutenant (Training Day is a close second, though, on how to end up in prison as a cop).
End of Watch
Saved my favorite for last. This is one of my favorite movies period, not just cop movies. The opening scene where Jake Gyllenhaal is talking about "We are the Police" is incredible…you're watching a police chase that turns into a shootout and at first you don't hear any sound…just him talking about good vs. evil basically. When he is done speaking, the audio to the movie kicks in and your adrenaline is already pumping! The movie shows how close we in law enforcement are. I work in a unit where we all have partners and this movie shows the camaraderie we have with one another, both on duty and off. Plus the officers are chasing gangsters throughout the movie, which is what my whole career has been. I will say this...I choke up EVERY TIME I watch the end of the movie. Couldn't imagine losing my partner and having to be at the funeral and speak about him.
(The soundtrack to End of Watch is great as well. Certain songs I hear like Camron's or Public Enemy from it always take [me] to certain scenes within the movie)