I'd like to add my vote here for Orson Scott Card and John Wyndham. My son who is now 13, enjoyed "Ender's Game" and "Ender's Shadow". John Wyndham's novels may start a bit slow for a young reader. In this regard "The Kraaken Wakes" is one I found hard to get into as a child. The "Midwich Cuckoos" or "The Chrysalids" are two that I would recommend, although some background explanation of the latter might be necessary for someone born after the Cold War. "The Day Of The Triffids" is perhaps, a bit dark. His short stories are great if you can find them.