I'll swear up and down that Mel Brooks' History of the World, Part 1 is by far one of the funniest, wittiest, most rambunctious movies ever made. The scene where Brooks is doing his stand up philosophy in front of Caesar is absolutely hysterical. Dom DeLuise does a fantastic job as the gluttonous Caesar. He really sells the scene.
In fact, many of Brooks' movies are solid gold. More recently, of note, is The Producers. I had the wonderful opportunity to see it on stage. I have to say not much is lost in translation from stage to film. Nathan Lane's dialogue alone is why it's worth watching.
Some others to watch:
Dirty Rotten Scoundrels (if for nothing else but the Prince Ruprecht scenes)
Johnny Dangerously
Superbad (mostly toilet humor, but it's really fast-paced)
Chasing Amy
Clerks 2
Other good color films with witty dialogue mostly have to be musicals.
The Music Man (a real treat, it combines visual and verbal wit)
Mary Poppins
My Fair Lady
Willy Wonka and the Chocolate Factory