The Avengers
I think when I saw this three times in theatres, I knew this would be one of those "I could watch this at any time, any day, no matter what" kind of movies, but having just watched it again just now, I think it's official. Fuck, I love this movie. While one could honestly nit pick it, it's in my opinion to be the perfect superhero movie. It gives you enough build up between characters to give a crap when they start fighting each other and then team up, it doesn't take itself completely seriously and realizes just how much fun these bigger-than-life characters can be, and just overall, fun.
A few things I realized watching it this time with Whedon's commentary:
1) Whedon is, and always will be, the king of entertaining commentaries. It's constantly informative and funny, and he's there to work, leaving little time for dead air.
2) He openly admits he hated doing the "cut the head off" ending, post-nuke, but said it was necessary to give them that final ending to the battle without having to clean up and keep fighting for another 17 hours.
3) He points out - quite rightly - that Hulk just comes out of nowhere during the final battle to do stuff. He leaps out of nowhere to beat up Loki and leaps out of nowhere to save Tony. And honestly, I doubt many will complain simply because it's the Hulk and he's already such a randomly violent character that it works.