Todi, Assisi, Cortona, and Orvieto are all just a few hours drive from one another, in Tuscany and Umbria.
For touring these towns, I recommend Cadogan guidebooks; our book -- which covered all of Italy -- had interesting stories and background about our destinations, as well as where to stay, etc. Cadogan also has books specifically on Tuscany and Umbria, and even on particular cities such as Assisi.
