TOD: I'm quite partial to "Holiday" and "Bringing Up Baby". I also rather love "My Man Godfrey", which is more social commentary than slapstick but it has its share.
I think "Sleeper" is a lot of fun, too, in addition to the oft-named (and beautifully cast in supporting roles) "What's Up, Doc?"
The sight of Woody Allen pretending to be an android and serving Dianne Keaton's guests is hysterical slapstick.