what is he into? video games or sports? or something else?
I think 10 is a good age for a computer, assuming he doesn't already have one.
If he doesn't have a video game system I would consider the XBox 360 with Kinnect.
Board games
legos
movies
tickets to see a professional sports game
equipment to play his favorite sport at home
a new bike, if he has outgrown his old one
rollerblades or skateboard
music MP3 player and money to download from an internet site
concert tickets (whoever gets them gets to tag along)
have him make a list, my family starts ours in july when their birthday's are done and they start asking for things I tell them to "put it on your Christmas list." There is always soooo much on the list they don't know what they are really going to get