Tuscany without a car?

Yes! Siena, Montepulciano, Cortona. Many more accessible by bus: Volterra, San Gimignano, Montalcino. Some are a bit distant from Florence, but you can easily do Sienna from Florence by train or bus. How many days/nights do you have in Florence? If you can spare a night, Orvieto is a marvelous hilltown on the way from Florence to Rome. Or stop there for the day on the way. You can leave Florenace at 0900, be in Orvieto by 1130, have lunch, tour and continue to Rome by dinner time.

cynthia, As the previous reply indicated, many towns in Tuscany are easily accessible via public transport. Do you have any ideas on which towns you want to see? You might get some good ideas on which towns to visit by having a look at the Italy Guidebook. Given the route you're taking, Siena would be a good choice, as it's "on the way". Travel by Bus is about the same time as by train, and is a bit easier as travellers are dropped in the centre of town, rather than the bottom of the hill where the train station is located. Although Orvieto is in Umbria, it's also an excellent choice as it has the same "character" as the hill towns of Tuscany. It has an interesting history and the frescoes in the Duomo are incredible. It's also only an hour by train from Rome. You didn't indicate the time frame of your trip or how many towns you want to visit, but these are a few suggestions. Happy travels!