I know it's SO hard to buy for boys that age - I had to do it in October, and had the hardest time.
I think Tyra's idea of a nice new set of headphones for his discman is a good idea (if he's into music). I know a boy who turned 13 in October, and he would have loved that.
What types of stuff is he into? Does he like skating (skateboarding or rollerblading), skiing or snowboarding? For skating you could get him a nice, new set of wheels from a skate shop - just ask for a good brand, and they should be able to help you. Or for skiing or snowboarding, you could get him a cool hat or goggles, but those can be expensive sometimes.
The thing is though, I bet he would have NO problem if you just asked him for a CD or two he would like. Sometimes that's a safer bet than gambling and possibly getting him something he'll never use.
You could just say, "hey, I got you one present, but I'd really like to get you something I know you'll love", and maybe he'll tell you (hopefully it won't be hundreds of dollars )
“When I let go of what I am, I become what I might be”