Well first thing to do InSane is to work out exactly which model of iPod he has. I brought a nano earlier this year, but each subsequent model is slightly different, so something that fits last years model might not fit this one.
Secondly does he spend more time in or out of the house? Buying him some flashy speakers probably wouldn’t do much good if he spends all his time on his BMX. If he doesn’t own a BMX then buy him one of those dammnit! They’re awesome! A Raleigh Tuff Burner should be your first choice.
Personally though I’d get him some top-notch, in ear headphones. I got myself a couple of these babies off of eBay:
CX 300 Silver
Plus, when you’re walking down the street, these don’t scream “I’m listening to an iPod! Mug me now!!!”