Can't really pick a single one... My most memorable "funniest" include Mel Brooks movies (Blazing Saddles, Men in Tights, Space Balls, History of the World Part I, Silent Movie, The Producers... All of them really.)
I also have to add Clue. I love that movie.
Hehe... I love those old Mel Brooks movies. Being born in 1971 I've watched quite a few myself. But seeing the title I won't list them all...
The Gods Must Be Crazy
The Naked Gun