Here are some of my recommendations for kids his age:
The Golden Compass: The first book was excellent, the 2nd book, less excellent, the third book just plain weird! I think if he reads the first one, he'll *have* to read the rest just because of cliffhangers.
Another good fantasy book is
Brave Story. It's really long, but full of adventure. It reminds me of a Japanese RPG (which is funny because I guess it was made into an RPG later) and it does feel very Japanese at times (the main character's not some happy-go-lucky boy who's always ready for adventure -- sometimes he's quite depressed).
Does he strictly want stick with fantasy? If not, I recommend the
Ender's Game series. I read it as an adult but wish I had read it when I was younger.
Steampunkish, but more like "let's have adventures on hot air balloon animals!" but I really enjoyed
Leviathan. Female protaganist, not sure if it matters, but she's disguised as a boy the whole time.