D.K.
One that we have used is:
"Thank you for the food we eat
The clothes we wear
Be present with us everywhere. Amen"
It rhymes and it's easy for little ones to remember.
Here's a new note about the post right above mine. That tune came from the old animated Johnny Appleseed movie. I love it when I was little and I was wondering if anyone knows how to get their hands on a copy.