bohemiancoast

If he liked the Westerfeld, you might also set him loose on the His Dark Materials trilogy by Pullman. The first two, at least, go haring along through the ever-thickening plot bunnies in a very engaging way. I'll second the recommendation for Archer's Goon in particular of Jones', also Eight Days of Luke, Dogsbody, and the Chrestomanci books. Pratchett's Bromeliad series was fun, though it's a younger read than most of the rest of the recommendations you're getting. For that matter, how about Jumper by Steve Gould? Almost anything by Daniel Pinkwater is good, though I'm particularly partial to the two Snarkout Boys books, which can be harder to find these days. Also Lizard Music.