I'm a teacher, and I'm always delighted when I see a parent asking for advice for teacher gifts. As I'm sure you know, teachers get a lot of stuff we don't really want.
You could get them each a large, beautiful, easy-care plant in an attractive pot, for their classrooms. I once got a gift card to Bachmann's from a mom, and I spent it on a lovely plant and pot. I think of that family whenever I see it.
You could get them each a gift card to a salon, for a massage or pedicure. We teachers love to be pampered, as it happens so rarely.
Or you could get them each several excellent picture books for their classroom collections.
Or you could give them each a gift card to Lakeshore to buy supplies and toys for the classroom.
The MOST important thing to do is write each one a letter telling them specifically how much you appreciate them and what they've done for your child. They will really love that.