Amaranth, brown rice, millet, spelt, kamut, quinoa.
This video also contains some interesting data on the progressive development of wheat leading to a more difficult to digest gluten content.
Sourdough spelt has a significantly easier to digest form of gluten that gluten intolerant people can tolerate. Not celiacs though.
Finish reading: https://www.youtube.com/watch?v=eFhhr7yLEds