Have a 15yr old girl with same problem, here are some suggestions:
I Home
Subscription to magazine (maybe a gaming one)
Season Pass for Amusement Park/Water Park close by
Flip Video Camera (check
Amazon, they have them for 89.00 on and off)
Basket full of favorite candy, snacks
Movie Gift card
Sweatshirt from school, favorite College. vacation spot
DVDs
Sports cards
Even though they are teenagers, they like silly things too. On another thread someone suggested the Marshmellow shooter, nerf gun etc., snowball maker, snowball shooter
I got my daughter a frog humidifier(she will love it), geometry for dummies, pig card game, Brownie pan with all edges. These will supplement the larger gifts.
They get tougher and more expensive as they age for sure.