My sister and I are going to be in Italy in June for 8 days. We are flying into Milan and renting a car.
We will first drive to Lake Como and Verona (1 night each) and then drive down to Tuscany.
The only place we are sure to hit is Florence and Montalcino. We have 4 nights in Tuscany and then heading back to Milan for the last two so we can shop. Any suggestions on places to visit in Tuscany and good places to stay? (farm stays or b&b is a possibility)
Also we are both very active and would love to know of some good bike trails or hiking, trail running areas.

I would spend at least one day in Lucca as well. From there you can move south to Siena, making a nice stop in Volterra. You can stay in the Chianti area (I would recommend this place: www.poderemarciano.it) and explore the area. Some suggestions include:
Pienza, Montepulciano
Monteriggioni, Colle Val d’Elsa (high area of the town), San Gimignano
Close to Montalcino: Sant'Antimo, Monteuliveto, Murlo

I agree with the previous answer concerning nice places to see.
I can add that if you like the sea, Elba, Giglio and Giannutri islands are beautiful, but they are a little bit far from Florence.
As for a place to stay in Florence, have a look at
http://digilander.libero.it/gorellik/villaridi