My friend's daughters love gift cards to "Claires", also - craft kits, gift cards to Barnes & Noble or B-Dalton booksellers, and Webkinz - always a hit.
The 13 year old is starting to get into makeup - and had been asking for things like shower gel & body lotion for the last couple of years. I feel like she'll have plenty of time to be an adult - so I always opted for more child friendly things - like the craft kits, gift cards, and webkinz. Also - jewelry- I've given them real (14K) small age appropriate earings, and gold bangle bracelets that they loved.