My comedy pick is the 2001 David Mamet film State and Main.
I'm surprised this movie is so under the radar, considering the all-star ensemble cast and the fact that it's hilarious. It came and went from the theaters without much fanfare.
State and Main is about a group of big-city Hollywood movie folks who descend on a small Vermont town to film a movie. William H. Macy is absolutely hilarious as the hard-ass director of the fictional film, and Phillip Seymour Hoffman is great as the innocent and idealistic screenwriter. Alec Baldwin plays the famous actor who is starring in the film, and who also happens to have a thing for underage girls.
State and Main gets a lot of comic mileage out of the contrast between the cynical big-city movie crew and the locals of the small New England town. It also pokes a lot of fun at the movie biz itself... the fictional movie being filmed ("The Old Mill") , is clearly terrible and seems to be a satire of horrible, Hallmark-channel-type wholesome family films. The self-importance of the cast and crew is hilarious in light of the terrible movie they are making. They act as if they are making the next Citizen Kane.
The main star of this movie is the rapid-fire comic dialogue by David Mamet. The jokes come fast and furious, and the entire movie has the feel of an old-fashioned screwball comedy or farce. Lots of fun.