A Simple and Romantic Gift
One of the things that I have learned since I started dating is that it is the thought that counts. Instead of buying your girlfriend something really expensive, something small or free can have the same effect. Now, I am not saying to be cheap by any means, but instead, be creative.
Creativity goes a long way and it helps her know that you are serious about the relationship. I quickly learned that buying a rose was not as good of a choice as say buying a plant since roses are such a common gift.
You can even just take the time to write her a poem and that will get you more "brownie" points than buying a gift as you took the time to do something special for her.
Whatever you end up doing, keep it simple and the value of your romantic gesture will be increased.