We will be staying in Florence in mid-September and have dedicated one day for a full day trip, via car. We have been to San Gimignano, Siena, Lucca, and Radda. Any suggestions for other must see day trips from Florence? We love Tuscan scenery but also enjoy smaller towns.Thanks

What about Pienza, Montepulciano and Montalcino? They're quite conveniently close to each other, while each being a little different from the others. Near Montalcino, I would not miss the 11th-century abbey of Sant'Antimo: an absolute jewel.

Montalcino, Montepulciano and Pienza are wonderful. But that's a lot of driving and little time at each. Adding Sant'Antimo will almost be impossible.
I think these are all great to see, but Florence isn't a good base to experience them.
That said,if you're game, leave early (especially before Florence's traffic backs up) head to Montalcino first, hit Pienza (lunch?) and finish at Montepulciano.
This will be a full day and you'll still need at least 1 1/2 hrs to return.

I love the beautiful city of Vinci. It's only about 20-30 miles from Florence and is set in beatiful Tuscan lanscape, quaint city and great Leonardo museum.

For something different there's Montecatini Terme, arguable Italy's most fashionable spa town. Set in a verdant park-like most un-Italian setting Montecatini offers several imposing thermal establishments where folks come to take cures dotting lovely parks and gardens. The crowd seems most upscale Italians; the town is stuffed with hotels and restaurants. Few mopeds running amok here so there is a tranquil setting. A few miles from Montecatini is Collodi, the small village of Pinnochio fame. Montecatini is a short train ride from Florence.

If you do not pbject to the one day price, and driving out of Florence, then the S-146 drive is the best in Tuscany. Take A-1 south to exit at Chiusi, but turn west for Montepulciano, then Pienza, and finally Montalcino. Leave time for the Abbey Oiliveto Maggiore on the way home via Siena.