Not many, I have to admit, mostly more technical stuff. I was going to suggest one called All Cats Have Asperger Syndrome, but then he might consider it a bit childish - it is great though, even I liked it at 34 years old (but then again I'm a big cat fan!)
Freaks, Geeks and Asperger Syndrome is supposed to be very good, although I'm still working round to reading it. It might be pitched a bit above his age level, but was written by a 13 year old, so it's very accessible.