Also the Stainless Steel Rat series - it's not as slapsticky as Bill, but still comedic.
djnattyp
Craig Shaw Gardner's Ebenezum/ Wuntvor trilogies are fantasy comedy.
Philip Jose Farmer (as Kilgore Trout) wrote Venus on the Half Shell as a sci fi comedy.
(On the topic of Kilgore Trout - that pseudonym is actually a character from several of Kurt Vonnegut's books - also mentioned in this thread.)
Yahtzee Croshaw (the Zero Punction guy) has also written several fantasy and sci fi comedy books - Jacques McKeown is one series.
Glen Cook, more famous for the Black Company series - also writes a fantasy comedy series - Garrett P.I..
Steven Erikson, more famous for the Malazan books - also writes a sci-fi comedy series - Wilful Child.
Robert Lynn Asprin also wrote the Myth Adventures series. Phule's Company is sci-fi comedy, Myth Adventures is fantasy.
Summary: 'Life is unfair', chortles an opportunist who benefits from an unfair system.
In this vein I'd also suggest the Laundry Files series by Charles Stross and the Arthur Wallace series by Jonathan Wood are very similar - urban fantasy, secret spy / police occult organizations, British humour