We discovered Pienza during our first agriturismo apartment rental just outside of the town in the clay hills of Southern Tuscany known as the Crete Senesi. Just down the road from our apartment were sheep in the fields... a sign of what this town is really famous for--Pecorino--sheep's milk cheese! (Pecora means sheep).
Strolling through the beautifully paves streets, you will come across shops for cheese, wine, clothing, ceramics and gifts. There are a good variety of both casual and fine dining places to eat, gelaterias and even bars and alimentari. There are many apartment and villa rentals in the town limits as well as agriturismo farm rentals in the surrounding countryside.
Pienza is about 50 miles south of Florence, 25 miles from Siena and 35 miles from Perugia. You could easily use Pienza as your hub for a longer stay in Tuscany, driving to the major towns. There are also many worthwhile villages in close proximity to Pienza: Montalcino (home of the famed Brunello wine), Bounconvento (a wonderful medieval walled town), Bagno Vignoni (a village built around Roman baths), Bagno San Filippo (a natural hot springs where locals bathe in the sulfur waters for free), Castiglione del Lago (a fortress castle town on the shore of Lake Trasimeno), and Cortona (of Under the Tuscan Sun fame).
But remember... don't tell anyone about this Tuscan town. This is just between us, OK?