I'm also heading to Tuscany in Sept and have been doing a lot of research on wine there. In Greve there is an incredible wine store named Le Cantine that has over 140 wines to taste. You buy a card for €10, €15, or €25, put it into a machine and then select the wine you want and for a small price you get a taste. When you finish, you can get a refund for the value left on your card. Of course you can also buy a bottle of your favorite there as well.

http://www.lecantine.it/cantineUtent...?cambialang=en

Click on "Tastings" and watch the movie.