Thank you for all the ideas and suggestions. This year, with the new house purchase, I was looking for something with a small price tag (the parents' group gave the teachers a large restaurant gift certificate from our fundraiser treasury.) In the end, I figured, can you ever go wrong with a book? Granted, there's always the chance they've already read it, but that has rarely happened to me, so I think it's worth the risk.
I gave each of Hazel's teachers a thank-you card, a small stack of homemade cookies, and one of my favorite books I read last year, Three Cups of Tea. It's a great way to go because there are always new books coming out and every year I'm sure to have a favorite or two, so it's never the same gift twice. By the way, I'm in a good run of books right now - it's very exciting. First, The Inimitable Jeeves. Then Guernsey, and now The Book Thief.