A gift certificate to a teacher's supply store is always appreciated. Teachers spend a lot of their own money on supplies for classrooms.
A gift certificate to a local restaurant is nice. It would give her a night on the town. I always love it when I don't have to cook dinner.
Or how about a gift basket that you make up yourself? What does she like a lot? If it's ice cream, put an ice cream gift certificate, toppings, and tie a scoop to the basket handle. You get the idea?
How about a candle? Or maybe a relaxation kit, with lotion, bubble bath, one of those wooden foot massager things, etc.
One of DD's teachers always asks for a small framed photo. He has the photos of his past students all around the room. If your daughter is in elementary school you might get a frame the right size for their class photo. Or have you had a field trip where you took a class picture? Blow it up and frame it. You could even take a plain wooden frame and hot glue on little wooden school decorations from Michaels.
Of the usual teacher gifts, I always thought the note pads and mugs were the most useful. Personally, I think teachers get enough of these predictable gifts, but there are usually some nice ones at teacher supply stores.