My sister is a teacher. She would always appreciate anything, especially a handmade card or something like that, and wouldn't expect a gift, but ones she has seemed pleased with are: gift vouchers (very kind, means she can get herself something as a treat), anything like stationery that she can use for school, a little jar of homemade cookies. She'll generally use toiletries, as long as she doesn't get too many.
She already has plenty of mugs, keyrings, socks etc, so those tend to go straight to the charity shop (though she appreciates the thought).
Not keen on personalised gifts, especially those which feature the child's name, to be honest - with the best will in the world, if she has 25 kids in the class, that's a lot of framed button art to find space for.
I always think that the best question to ask when considering a gift option for a teacher is "If I received 25 of these in one day, would I find a use for them?".