Lamb is super good. It's in my top 10 books of all time list for sure.I'm a fan of Christopher Moore, I've read three of his books so far: Lamb, Coyote Blue and A Dirty Job. I have Serpents of Venice, Bite Me and You Suck on deck.
Dirty Job was awesome. I read the sequel (Secondhand Souls I think) a few weeks ago. It was also very good. One of his best sequels in my opinion.
Fool is fucking phenomenal. It's up there with Lamb. I highly recommend it.
Bloodsucking Fiends is great. Bite Me, the sequel, is... okay. You Suck (part 3) is sorta like fan fiction. Not his best work, but it's fun to see the characters again.