Gail Giles, author of a number of edgy (not hilarious) YA novels, including Shattering Glass. She's also got a wicked sense of humor: Here's her blog.
Also, Carolyn Crimi. She's the author of a number of hilarious picture books, including Don't Need Friends and has a great article on her site about celebrity authors (scroll down).
Until they get around to theirs, though, the Wilmette Public Library has a bibliography called "Comic Relief: Humorous Stories from Junior High Fiction." (And thanks to WPL for putting NINJAS on the list!)