Tom Holt is one of the masters of comic fantasy, and as the author of thirty novels in this genre, you've got a wide variety to choose from. His only real ongoing series, however, is the J.W. Wells company books, which make magic... rather corporate, and absolutely hilarious. Photocopiers that can only be worked by the seventh son of a seventh son? Always gets me. His books typically end in a convoluted confusion of plot - there might be holes, but it's always funny. However, his characters aren't as differentiated as some of the authors I prefer - several of his male protagonists seem to merge after a while, so if you're inclined to focus on character rather than comedy... Well, you'll still enjoy his novels, but perhaps not quite as much as otherwise.
If you're planning on starting Holt, I recommend the first in the JWW series: The Portable Door, which can be found on Amazon here - The Portable Door
How could I possibly write this without mentioning Pratchett? The Discword is a setting that works mostly on narrative, and Pratchett's characterisation is fantastic: his humour is generally subtler than the other authors listed here, and he deals with more serious themes and issues as well, tending towards satire and deconstruction rather than outright insanity (Rankin). You've similarly got a large variety of stories here, with recurring characters and groups such as the City Watch, witches, and wizards - as well as spin-offs like The Science of Discworld - which I'm reading now. If you haven't read Pratchett... Well, let's just say that this needs to be remedied. Now. Personally, my favourites are the Moist Von Lipwig books, which focus around the involuntarily reformed conman-turned-public-servant, the first of which you can find on Amazon here:
One of my favourites, The Brightonomicon, can be found on Amazon here: The Brightonomicon (Brentford Trilogy)
Read these books, or have any suggestions for others I could add? Comment below and tell me!