a cute necklace if you actually like her.
Definitely not something too romantic. What are her interests that she's expressed?
Notebook is a great idea. A small leather-bound one, something unique. Forget DVD's, too 'friendly' I like to think. I'd say notebook or a nice calligraphy pen set if she likes to write fancy/draw.
Have her sign a prenuptial agreement. It makes a great Christmas gift.