I usually don't look for books aimed to be funny, since they tend to border on boring and dull, but two books that had me snorting and giggling are listed below:
The Bartimaeus Trilogy (I loved the guys wit, at least in the first book: two and three had it, but veered more towards plot than humor, which is fine: the book is fucking awesome, if you haven't read it, then you better)
The Alphabet of Manliness (I loved the guys website when I was younger, gave the book a whirl, the jokes were very dry and adolescent, but that didn't take away the fact that me and my friends loved them)