Little Brother is hands-down the best young-adult sci-fi I've ever encountered. It's quite recent (within the last year), and is Creative-Commons licensed, so you can check it out before buying if you so desire. The writing is excellent, the story top-notch, and it's chock full of technophilia and anti-authoritarianism. Might be a bit too dark for pre-teens (judge for yourself). Everyone should read this before high school. I say that without reservation. http://craphound.com/littlebrother/ (Also, I second the recommendation for Invitation to the Game. I liked it.)