What are her interests? I for one prefer practical gifts. Not chocolates or flowers, which won't last a week (I see these as secondary things that complete a gift), but something she can use for a long time. Since she manages the bird collection in a local museum, and plans on becoming an ornithologist, I'm getting her a book on Birds of Venezuela (which ironically can't be bought here in Venezuela!). She's lusted over the book for a few months now, and in a week she'll be reading it

I can be sure no one is getting her the same thing.
Bottom line is notice what she likes, or if you've payed attention when you've gone out she'll probably have told you that she liked something. Not directly (that almost never happens, so don't hold your breath), but she has probably said "this is cool" or something like that...
Now that I think about it, how about a shuffle? preload it with some songs she likes (or that you want to dedicate her) and it'll be a great touch. Heck, if things are going really well, record a personal message for her, rip it to MP3 and put it on the iPod
Think about her interests, what she likes, what she'll find useful and you'll come up with something. Is she working at something particular where she'll find an item useful? can something she already does be "upgraded" with an aditional gift? For example, if she listens to a lot of podcasts (or music, for that matter), she might like over-the-ear headphones that are much better than the small ones she has now.
I'd be happy to continue brainstorming