Here are four ideas:
1) A charm bracelet: each charm signifies an important place or thing or interest that is meaningful to her. You can add to the charm bracelet each year.
2) Cook a really nice dinner and don't forget the decadent dessert.
3) Buy her a day at a spa.
4) Buy her the high heels she's been drooling over.
Mostly, women just want to feel special. It's not a thing of buying expensive things, unless you can afford it. (You also don't want to be a cheapskate, either).She just needs to be reminded that you care and that you believe she is the most amazing woman you've ever known. Be sure to write that in a card... or something along those lines.