I agree with skyKitty, Lego is great.
If you don't want to get her toys how about a camera, I gave my eldest DD a camera when she was 6 and she loved it and still uses it. She takes it to school on special occasions and takes lovely pictures. However my youngest DD is now 6 and wouldn't be too impressed if she was given one!
Books. Not necessarily story books, you can get great books for children on cooking and craft etc....
Vouchers. My girls would be excited to be given vouchers or cash and let loose in a toy shop to choose their own gift.
As part of her present you can get her membership to one of these online games like club penguin or Moshi Monsters and Virgin and Toy Store have the trading cards and books that you can also give her.
What about a special day with mummy, you could transform your living room in a beauty salon for a day and do your nails and stuff or go to the movies and a meal just the 2 of you. My dad has no money and wanted to know what to he could get for my half sister's 11th birthday and I suggested they'd go for a walk just the 2 of them as they don't spend that much time together and I knew she'd love that.
If you get a kitten/puppy
a) make sure you a re very very serious about keeping it for its whole life
b) try to adopt from Feline or K9 Friends
Pets are great for kids to learn responsibility, but if you can't take it with you when you leave... better to get something else.
If she into "hands-on" things, how about Lego? I LOOOOVED my Lego at that age and still have great fun playing it with my little cousins. You can get girls' versions too that become doll houses etc... plus if she has a little bro or there are boys in the street she can still play together.
I still have my Legos in a box at home for when my sister's kids stay.