I bought Underarmour gear this year for my 5 male cousins (ranging in age from 13-18) that I have to buy for (don't ask). I've also done iTunes gift cards and movie gift cards in the past.

I think you should start by asking his mom what he's into.

I have a 15 year old that also has a birthday soon after the holidays. This is what he is getting for both.

Clothes (Pac Sun, Zumiez, A&F, Holister, American Eagle, Abercrombie)
new soccer cleats
Adidas sneakers
underarmour stuff
laptop
CD player and blank CD's (he's into burning CD's)
socks (from stores like Pac Sun and Zumiez or athletic ones from Adidas or Nike)
tickets to a show (hip hop artist he likes - he will go with his dad)
Chipotle Gift Card
Store gift card (from one of the stores listed above)

iTunes gift cards.

Take him to an electronic shop and pay for something he chooses

Movie passes. Hoodies. Sports jersies. If they have a bike - cell phone holder for the bike.

Cash

Help, my nephews are visiting over the holiday, and I have no idea what such young men would be interested in!

What do kids like these days?