ultramarina, Thank you for your post. I feel like I am in a very similar situation with my 10 yo DS. His preference is fantasy. Among the many already suggested including Enders Game, Hitchhikers, Rick Riordan series, Gregor series, Tolkien, my son has enjoyed:
The Secrets of the Immortal Nicholas Flamel (6 Books) Michael Scott
The Keepers (3 books so far...) Ted Sanders
The Thickety (4 books) J. A. White
City of Ember (4 books) Jeanne DuPrau
The Secret Keepers - Trenton Stewart Lee
What If?: Serious Scientific Answers to Absurd Hypothetical Questions - Randall Munroe
DS is currently finishing Watership Down.
Keep the suggestions coming... lots of good new titles to research, thanks.