I think it's so cool that you signed up on this site just to ask what to get your GF for Christmas! Brownie Points (from me at least) on that!
I would either go w/ a gift card/prepaid Visa, or the "take her shopping & to dinner" idea. If it was my DH, I would definitely not want him picking stuff out for me, simply b/c I have so much & he'd probably get me something I already had when I'd rather have had something different.
Good luck & if she isn't already a member, tell your GF about this site!