In preschool and kindergarten, my children painted a clay pot and we planted a geranium for their teacher in it. Then they made a card and we enclosed a Barnes and Nobel gift card in it.
From my older children, they make a card and we put in a gift card.
As a former teacher, let me give you a couple of words of advice.
1. Something made by the child is always better. I haven't taught for 10 years, but those are the gifts I kept. they help me remember each of those children.
2. Gift cards are great!
3. Don't forget those teachers who teach things like art and music and see your child a couple of times a week. Maybe not a gift card - esp. if your budget is tight, but a hand made card from your child will be appreciated!
I agree, that handmade/homemade is always great!