No Good Omens? Well, that means you've read everything...
Only kidding, MoonCat. I'd actually put money on that being one you have read. It was just a roach-like response that had to be given!
And, for the record: Neil Gaiman and Terry Pratchett are my two favourite authors of all time. Well, writers. Well, storytellers. (Neil, you're a multi-media pain to the cataloguing system.)
Rich is just below them, would you believe, sharing a tied-space with Ursula Le Guin and Daniel De Foe? (Yes, I'm weird.)
If we're talking crossovers: I've die a nerdy death of happiness if Terry Pratchett would allow Sam Vimes to join CPPD for a day in the PDF limelight... Or, I'd settle for Nobby. And, Colon, natch.
EDIT: Actually... Nobby might work as an incredibly improbable half Orc-Halfling combo. Particularly when you bear in mind what his father was like.