Bicycle
If he hasn't got a bicycle, get him a bicycle. Bikes are great presents. Fun, fitness and freedom are the benefits he will get from a bike.
If he already has a bicycle, has he got a cycle helmet? They really are lifesavers. In America, laws in 21 states and over 145 localities now require bicycle helmets. A good set of lights and reflective clothing for when he is out riding are also good presents for a boy.
Best to find out what sort of bikes he likes though. There is a big difference between a BMX and an off road trek bike. A third option is the Lance Armstrong style road racer, but I suggest you don't make that decision without his input.