Azayzel, you might like Christopher Stasheff's
Warlock In Spite of Himself and sequels. Also, try C. Dale Brittain's
A Bad Spell in Yurt etc., and possibly Patricia Wrede's "... with Dragons" books, T.H. White's
Mistress Masham's Repose and (for a switch to SF) James White's "Sector General" books (medical mystery humor SF -- that enough combinations for you?) I think you also might like
City of Baraboo,
Elaphant Song, and
Circus World by Barry B. Longyear, which are just recently back in print. I'm sure you've already read Douglas Adams.
And obviously, if you haven't yet read
Good Omens by Neil Gaiman & Terry Prachett, run, do not walk, to your nearest bookstore (or internet connection) and get yourself a copy. Possibly more than one.