I have a Sister who was just 8 and I am absolutely useless when it comes to buying presents for kids especially of the opposite sex, since she was 3 I have always bought her a gift voucher for Toys R Us, while not all that exciting on its own, it has the added excitement of the kid then being able to go and choose a toy out which extends the time the gift takes to wear off a bit.
I always get a thankyou note from her telling me what she has bought which often the name of means naff all to me but at least she's happy

And for the last 2 or 3 years she has written the card herself, her writing is amazing, how is it that girls excel in stuff like that over boys?
Anyway, hope it gives you an idea