I had a wonderful gluten free meal at:
Osteria Il Campino, Via Vittorio Veneto 29, 53100 Siena (Tel: 0577-236545).
The restaurant had a wonderful selection of GF dishes, and I was excited to see a GF pasta dish on the menu and a couple of desserts that I could enjoy. They even provided me with gluten free bread to accompany my meal. Our waitress spoke English and was very helpful indeed. I inquired where I could purchase some gluten free bread nearby and she told me that the main distributor of gluten free products in Italy is a pharmacy. Before we left the restaurant she packed up the remainder of the loaf and gave it to me. I was truly touched by the gesture. I highly recommend this restaurant. Prices were very reasonable.