Is there a good joke/comedy/humor database or "thesaurus"/"dictionary"?

I'm trying to sprinkle some more humor in my writing. I was wondering if there was a good database out there to look up jokes or clever witty quips according to topics or keywords. When I was experimenting with songwriting, I found some great resources for looking up rhymes, references, alliterations, etc. I was wondering if anything existed specifically for comedy.