I've played three games which I would consider humorous: Toon, Gamma World, and Paranoia. Toon was a very long time age and I don't remember it much. Cartoons aren't my thing anyway. Gamma World was also a long time ago and it had limited appeal for me. But as I've mentioned in earlier March Madness posts I love Paranoia so that is definitely my number one pick for humorous.
I love the puns, the sarcasm, the mocking of just about every political ideology, the way everything is deliberately designed to be some sort of trap. And yet it is extremely flexible in putting together all sorts of ridiculous plots and situation. I also love how most of the action is driven by player interaction. It's almost a vehicle for comedy improv acting.