Chianti Classico wine festival - every year on second weekend of September and the preceding Friday, 10 - 12 Sept 2010. On Friday, the festival starts at about 5 pm, and on Saturday and Sunday at about 11 am and the stands close at about 8 pm. The idea is that you buy a wine glass from the Segretaria (price in 2009 was 10 euros) and are then free to taste any and all wines offered at the stands. I have heard but not seen that they can run out of glasses.
Chianti Classico Festival des Vins - la Programme pour 2010