For the last two years my son had teachers who had young children. At the end of the year I gave one of them a sand pail that I filled with things they could use to have fun in the summer ie: bubbles, sidewalk chalk, kite and a gift card for local fun center. The other one I made an ice cream sundae bag and gave cute dishes, ice cream scoop, toppings and gift certificate to Friendly's to buy ice cream.
Another teacher I know loved chocolate so I gave her a bunch of chocolate items, candy, brownie mix, mudslide mix etc. They all seemed to like them.
Another year I got these silly plastic cups from the dollar store and put in a tub of crystal light drink mix and a Barnes and Noble gift card and a note that said something like enjoy a cold drink in a cool cup with a great book. Corny I know!