Time to be controversial: The Dark Knight
Okay, this is a personal one for me. I'm not denying that the proper ending is a very good, emotional bit of filmmaking. But for me, from my standpoint on this film, it just didn't need to happen. By all means, have the whole thing of tearing down Harvey Dent to the level of the Joker, but for god sake, having 15 minutes AFTER the Joker is aprehended to showcase Harvey threatening to kill Batman, himself and a small boy just because Jim Gordon didn't know there were traitors in his office who helped in the death of the woman Harvey had known for a month or two and who had only bothered to accept his marriage proposal when faced with certain death.
The entire scene is just Harvey taking "whiny little *****" to the utmost extreme, and I just didn't need to see it.