I second the Moore (especially Lamb) and Fforde recommendations, and thank Wintergreen for the Tom Holt nod. I'd heard of him, but didn't know he was in the same category of writing (whatever the heck that is, lol)
As for Good Omens, I really loved it, but, as someone up there said, it takes some 'referring back to' the earlier chapters on the horsemen once things start moving. I've got it on my 'to reread' list, for that very reason. I don't think it took much away from the book, it just bears rereading... then again, I'm biased because I'm a sucker for that sort of novel.
It's been a year or 2 since I've read it though..I'll have to request it again and give it another whack soon.