Apologies if you have already covered these.
When mine where that age I put together skin care baskets (cleanser, toner, pads, wipes etc) I had already purchased the make up on their wish lists, so this was a good addition.
Also at that age they were starting to go on sleepovers with friends - so I brought an overnight bag with matching toiletries bag, new PJ's, dressing gown, slippers, bed socks etc.
Another idea could be a "movie night with friends" - DVD, packs of popcorn to pop, chocs, and a voucher for a bottle of pop. Get some invitation cards to invite friends.
What about a "hobby pack" - one DD loved to draw, so brought a pack of artists pencils, charcoals, pastels etc - she loved that.
Gaming vouchers or subscription (Xbox live etc)
I used to keep an eye on things they were interested in leading up to Christmas and work it out from there - but will agree, it's hard getting it right. Sometimes the present I thought they wouldn't like often turned out to be one of their favourite things!
Good luck