If you are in Florence this weekend there is a wine tasting event centered around the Piazza Pitti and other locations of the oltrarno (the other side of the Arno). €10 for the glass will get you 16 tastes from many popular wineries. We suggest trying the following: Casale dello Sparviero (a small producer from Castellina), Castello del Teriiccio, Il Borro and Villa Mangiacane. There is more information here.