"Must See" villages around Tours France

As we tootle around the Loire Valley (broad, vast area I know... i'll whittle it down in a sec here) looking for Castles, we also want to stop at "Must-See" villages... you know, the ones you unknowingly pass up on the map. Follow the Loire river from Usse in the West, up to Blois to the East, and then hop down to Loche in the South, and that's our tourist scalene triangle.