Weekly open air Markets
There is a market every day but Monday in the Chianti area

Tuesday - Poggibonsi/Figlini Valdarno - these are markets for the locals so you will need to use your elbows!
Wednesday - Siena - a large market recommended for shoes, bags, and clothes but get there early, opens around 07.30.
Thursday - Montevarchi - very useful
Friday - Colle Val d'Elsa - the market is in the new town, the old town above is well worth a visit too
Saturday - Greve - a delightful market square that buzzes with activity, a pork roast normally arrives at around 10.00 still sizzling on the spit
Sunday - Panzano - small but good, in particular there is a excellent specialist of Tuscan salamis and cheese.

Other periodical markets of interest
Arezzo - this is a famous antiques markets held the first weekend of every month, if you like antiques you will love this market
Radda - held the weekend of Easter, exclusive and chic
Florence - the San Lorenzo market is every day and open the whole day.