Se7en
Wow. As a fan of crime thrillers I can't believe it took me this long to watch Se7en. The whole atmosphere is extremely chilling, and Fincher does a great job of keeping you on the edge of your seat. Kevin Spacey has a certain smugness in the back of that police car that had me making wild guesses on what the final twist was. Theres a reason this film is a monument in Fincher's career as it is just beautifully executed and shows the brilliance of David Fincher. I loved Brad Pitt and Morgan Freeman so much in this film, and am in awe by their performances.
Also I just realized in my effort to watch a film everyday in the month of December, I decided to watch Se7en on the sixth... fml