Start with the things you know she's into. Think about it, and come up with something appropriate.
For example, my wife's been getting more and more into gardening. For her, planning landscaping and working in the yard is both a creative and therapeutic outlet. (Meanwhile, for me it's a pointless and mind-numbing duty.) So one Christmas her main gift was a hefty gift certificate at the local garden port. Big hit -- she didn't expect it, but it clearly showed I was paying attention to what was important to her. Before that she got interested in bird identification, so I got a fancy birdfeeder system from Wild Birds Unlimited -- set it up in near view of the kitchen window and left it for her to see on Christmas AM. For her birthday got a good bird ID book.
So if she's into music, check out when her favorite group is coming to some nearby venue and pre-order tickets. Etc, etc.
If you can swing it, a getaway weekend can be good too, especially if its to some place you know she'd like but SHE knows you're not hyped about. (Where I live an example might be a bed and breakfast trip to amish country.)
