get her wot she wants or needs. ask her or watch her carefully
to find out...
somthing she will remember but somthing she can be by all the time such as julary
It Depends What she likes, how old she is, and If your a friend, parent or boyfriend/girlfriend.
For something special try making a collage or photo album of photos of you together, or even a mix CD of your fave tunes. Clothing, jewellery music and shoes are always nice too. For a safe bet give her money.
If she's mature give her an ornament or artwork.
Hope I helped :)