I love humorous novels, but they seem to be hard to find. Here is a list of some funny fantasy and science fiction authors.
Terry Pratchett – Consistently amusing.
Douglas Adams – Classic.
Christopher Moore – I liked his Coyote Blue the best so far, although I haven’t read all of his books yet.
Patricia C. Wrede – Fun.
I know I’ve forgotten a few. Feel free to add your own recommendations to this list in the comments.
Josephine L Brooks 
Douglas Adams is the FUNNIEST WRITER I have ever read. The Hitchhiker’s Guide to the Galaxy series…. literally the funniest thing I have ever read.
He is one of my favorites too. 🙂
What do you think about Jonathan Stroud? I know his work is more dark humor… but I think it’s great!
Ooooh… I like dark humor. I will check him out! Thanks for the recommendation. 🙂