We are planning an October trip to Tuscany. If you could choose five "must see" towns (excluding Florence) what would they be?

Pienza
Montepulciano
San Gimignano
Montalcino
San Quirico

You'll love Tuscany!

in all honesty i think san gmignano is over rated and over seen......but then again, at least it will be palatable in october.
but dorkeforcemom has a good list
in addition
i like volterra and lucca.....less touristy and yet still very tuscan

Siena
Lucca
San Gimignano
Pienza
Montalcino

I'd vote for Siena, San Gimigiano, and Pienza. I know that's just 3, but I'll ask DD (who was studying in Siena) for others. While San G. is very touristy, it probably is that way because it's so incredible. Be sure to climb to the top of the highest tower--the view is how I always imagined Tuscany to be.

rpowell,
If it is the end of October see http://www.montalcino-tuscany.it/sagra_del_tordo.htm Send me an e-mail and I will send you information on many Tuscan towns.

Henry

Sienna, San Gimignano (not overated) some small towns: Sant Antimo - go to the Abbey and hear the monks sing Gregorian changes, its just outside of Montalcino.
Murlo - visit the museum and eat at La locanda del castello - have the house wine.
Travel between Buonconvento and Montalcino and stop at the winerys and taste.Great little restaurant just outside of Montalcino is the LaCrociona.
Pienza and Monticchiello - can see both.

All the above,plus many not mentioned. In Chianti add Greve, Castellina, and Panzano.
If yoiu see San gim,don't skip Volterra.

Pienza
Lucca
Montepulciano
Castiglione d'Orcia
Pitigliano/Sorano-not actually in Tuscany, but very close

Not too crazy about San Gimi

walled adjacent towns of monteriggioni, volterra, and san gmig, sienna, lucca, manarola/cinquer terre, and florence--see my 2003 report on trip advisor; of course, if you wanted to to see the chianti area, throw in radda.

I will be staying in Florence and I plan to take a day trip to San Gimignano. Is there a bus or train that would provide day trip transportation?

You can bus to San Gim,but with a stop.
Here's a website that helps:
http://www.sangimignano.net/bus/

There are so many, but so far, I haven't seen any that I'd replace to the list that dorkforcemom gave -- that's pretty near perfection for me.

If you hadn't said "small towns" then Siena would go onto the list, though. And perhaps my next choice for #6 position would be Cortona.

Volterra, Montalcino, San G., Montepulciano, Pienza...