Several years ago I had the pleasure of watching the movie Bringing Up Baby, one of the best screwball comedies I've ever seen. Starring Katharine Hepburn and Cary Grant, it's the story of a paleontologist (played by Grant) who gets caught up in the world of a free-spirited young lady (Hepburn) who needs his help dealing with a tame leopard, a missing dinosaur bone, and her growing fancy of him. He just wants to finish building his brontosaurus, secure funding for his museum, and marry his secretary (all in one day!).
I'm seriously underplaying the story, but it's a madcap romp (and how often do you get to say that these days?) that builds and builds through the entire film until you're laughing throughout the ending of it. It has great improvisations, sharp humor, and wonderful slapstick sensibilities with two extremely classy actors leading the way. Cinecollage.net describes a screwball comedy as "sophisticates gone silly," and that truly is what that movie represents.
In 1972, a spiritual successor came out starring Barbara Streisand, Ryan O'Neal, and Madeline Kahn called What's Up, Doc? I watched it over the holidays, and while I found it to be a great successor to Bringing Up Baby, I think it slipped a few times while trying to reach such lofty goals.