Dude, you don't need to buy a ring for her. And dump the idea of a necklace. Be unpredictable man[crap, I'm reminded of Eurotrip]... Do the crazy things, not the cliche.
Get her a present that is beyond the ordinary. Well, your present doesn't have to be spectacular or really expensive. Something original, sincere, unique and interesting will just do fine. And for that, I can't give you any advice. You've got to rack your brains for ideas.
Although I think writing a song for her works... And don't forget flowers. Girls adore flowers. And lastly, just go to her house to pass the gift or do whatever you wanna do. It's sincere man.