Yes, the cutesy crafts are super adorable and teachers very well may delight in wonderful yet time-consuming creations, but really you can't go wrong by sticking with simplicity here. And it's much less stressful.
Read the list below and pick whatever speaks to you, make it pretty with paper or a bag, and promptly pass it off to your kid to hand over with a big smile and a thanks. Because this celebration is not about finding the most spectacularly creative, punny gift idea or spending hours tracking down supplies and making said gift -- it's about showing that you recognize the magnanimity of their contribution to your child's life.
And nothing says thank you like donuts.
Bring in a dozen donuts (or fruit salad) for the teacher's lounge.
Give a gift card to a local coffee shop or a bag of ground beans and some creamer.
Pick up a bottle of good wine or liquor (only if you know they imbibe).
Grab a certificate for a 15-minute massage at a nearby spa.
Ask if they need any classroom supplies and go buy those.
Flowers are also probably good if they're already in a vase. And please note: most of these ideas do double duty as well-received Mother's Day classics as well.