In reply to Removed User:
To the list, I'd add Eoin Colfer's Artemis Fowl books
Maybe some younger Terry Pratchett, like the Bromeliad or the Johnny Maxwell trilogy. Neil Gaiman has some young stuff too, The Graveyard Book for example.
Adding to the classics suggested; at his age I was enthralled by the world described in Rudyard Kipling's Jungle Books, (plural) including the lesser known tales like Rikki Tikki Tavi and Moti Guj-Mutineer.
Somebody suggested that if he likes Willard Price that he could soon move onto Wilbur Smith; I respectfully suggest avoiding Wilbur Smith, many of his books are very adult-themed, with graphic sexual violence. (I wonder what it says about me that I have all his books) Jock of the Bushveld, also set in Southern Africa would be better for a kid.