Ok, so I have some fairly recent experience with this...I have 5 little cousins whom I adore, and always go all out for them for X-mas (partly cuz I feel guilty cuz I don't see em very much anymore)...anyway, 3 of em are girls...this year, one will be 15, the other two 13, so I'll tell you some of the things I have gotten over the past few years for them.
The year before last was the big hit...I was able to get lava lamps, and a couple other cool little light up novelty items for thier bedrooms..they LOVED them. I got other things, but can't remember what. Last year I got some little chapstick sets (with candy flavors, like 'Juju Beads' and 'Tootsie Pop')...little soap sets that were decorative and smelly (good smelly)...I think they looked and smelled like lolipops, or something. Aroudn that age, they are starting to grow up a little, and they are VERY subject to wanting the cutesy little 'make-ups' and things like all their friends have. I also got each of them a small bottle of a fairly inexpensive perfume, because all of them had already started experimenting with make-ups and perfumes...I think I got them Adidas Adrenaline for her. It's not too expensive, smells good, and pink, which a lot of girls that age seem to love.

This year, I got a good deal on a bunch of novelty-type stuff for their bedrooms again (coudn't pass it up at 90% off).
When I talk about novelty lights, I am talking along the lines of things like this:
These aren't the exact things I got, but along these lines.
If I can think of other things, I'll let you know...hope this helps a little.