Things to do/see near San Giamignano

I would definitely take a day trip to Volterra. It's not that far from San Gimignano and it's a very interesting town. We enjoyed visiting the Etruscan Museum there as well as seeing the alabaster shops/artists. We also took a half-day tour there (Annie Adair was the tour guide, from RS video) & found it to be extremely informative and fascinating. It's really a great town! I'm assuming you'll have a car as it's easiest to get around the area with a car. We also really enjoyed Pienza for the cheese (the Pecorino to be exact). I loved going in all the cheese shops and sampling the various types. I fell in love with the Pecorino Fresco and still long for it. Have a great trip!

There is a tiny little village/winery in San Donato which is very near San Gim. It is up a hill and has a beautiful view of the surrounding hillsides and vineyard. There is really no town, just a few b&b's and a winery, but it's a charming little place to wander around and look at the view.
Also, you are close to Certaldo Alto which was another fun little place... a few restaurants, shops, church, but a bit less touristy than some of the other towns.

By all means, visit San Gimignano and Volterra on day trips. There are many other hill towns closeby that are great, including Certaldo. Florence is just about 1/2 hour north. Tours to wineries and cheese factories are also popular. You can also take a cooking lesson. We liked getting out and just driving around rambling thru the countryside looking at the hundreds of small hill farms. I was surprised that there was not more English spoken outside of the tourist cities. It didn't matter to us. Some of the cities didn't have many places where we could eat reasonably.
We cooked most nights in our apartment after purchasing food in Certaldo and the two incredible supermarkets in Poggibonsi. We'd often picnic when out on our day trips. You will have a great, restful trip.

Thank you all for your suggestions. Yes, we will have a car to tour the countryside. It sounds like some days we might just head out in a direction and explore various towns. The comment about not finding many restaurants or reasonably priced ones is curious to me - I had the impression that would not be a problem in the small towns but perhaps we have to re-think that one. Would anyone have an opinion on using the train rather than car to spend a day in Florence? Again, I had the impression that it would be easier to leave a car at the station and train into the city. But someone said it is only a 1/2 hour drive?

Loved Pienza, as Sheron mentioned... also loved Montalcino and Montepulciano.

Good idea to take the train to Florence. Otherwise you may join others who come on to the Forum having received notice of a fine in the mail for driving in the city centre! Florence, along with most other towns and cities in Italy, limits who can drive in their ancient centres. Read up on ZTLs (Zona Traffico Limitato).