Well, it's awfully hard to rank really classic shows like Fawlty Towers, Seinfeld, and the current gem Arrested Development, but all are knee-slappers and brilliant in their own special twisted way. I gave my wife the boxed set of Fawlty Towers videos for Valentine's Day some years ago and we still enjoy watching them. Some really inspired episodes in there. Whenever we visit Germany you can bet one of us will caution, "Whatever you do, don't mention the War!"
Highly recommended.
My favorite moment from that entire series is when Basil's car breaks down and he starts raving. He goes out of camera sight and the next thing we see is him waling his car with a tree branch, yelling he's going to give it a damn good hiding or thrashing.