I'm going to Florence in September and would like to take a couple day trips--one to San Gimignano and Siena and one to Lucca and Pisa. We don't have a car. Does anyone know or have any experience taking the train or bus to these places? There will be nine of us. Any advice is appreciated!!

Train to Lucca and Pisa is easy. Bus to Siena is easy (and better than the train since it drops you in the center of Siena instead of outside the walls), and I don't think it's too hard to get from Siena to San Gim by bus. The problem will be herding your 9 people.

If there is a bus from Florence to Siena then you might want to take it since it drops you off right at the center.
However, the train ride was beautiful and the few times we went we just hopped in a cab from the train station - a couple of euros and we were in the hustle and bustle.

As a heads up (which I am sure every traveler has a story), I was pickpocketed while seated, waiting for the train to depart from Firenze SMN. I was seated with three other people and none of us noticed anything missing until I looked down and realized my wallet had been taken out of my purse - which was underneath my coat, in between my room mate and I, away from the aisle. If you think something fishy is going on, it probably is. I ran off of the train and chased the two guys who had taken my wallet and got it back, so don't hesitate to do the same - they rarely expect people to go after them.

One more thing, you hadn't listed Fiesole as a place to visit, but it is definitely worth a few hours of your evening. Take Bus 7 from the station at SMN, it is about a 30 minute ride up the hills surrounding Florence and once on top you have an amazing view of Florence and the sunset, as well as an amazing restaurant: PERSEUS. (I am going back next week during my trip back to Florence and can not wait!)

Wow, thanks so much for your advice...I'll check out Fiesole; I've heard it's great. I'll also have dinner at Perseus if we can. Do you by any chance remember what bus takes us to Siena? I'm trying to get every little detail buttoned up. Thanks again!