You must know what she really likes to have...what is her fashion? If you wanna give her a material thing, just be practical...ask her what she wants to have...I'm sure she will be happy. If she will tell you she doesn't like anything, you can treat her in a romantic dinner in a nice hotel/ restaurant....or give her a surprise party at your home....or maybe a round trip ticket for both of you to a country where she fancy to visit.