General information:

APT, official tourist agency - Check out their bricks-and-mortar location, 56 Piazza del Campo where they can provide you with maps, information of all kinds and, my personal favorite, walking guides to the different neighborhoods within the city walls.
Expatsinitialy.com --Very good online resource for the independent traveler contemplating either a long-term stay in Italy or living in Italy permanently.
Gambero rosso -- An excellent source for information on the food and wines of Italy, the quarterly magazine is very reasonably priced and in English. The website is nicely done, and much of it in English and easy to use -- some of the information is available for download via PDF.
Need to check e-mail while you're in Siena? There are a number of easily accessible access points in Siena. We used Internet Train with three locations in Siena, 121 Via di Citta, and 54 and 59 Via Pantaneto. More. . .Into Italy -- An excellent resource if you need help in finding English-speaking businesses in Italy, as well as a variety of other classifieds for the English-speaking traveler.
Italymag.co.uk -- Available in the US in print form but outrageously expensive this is nonetheless a very good online resource covering a variety of topics in Italy for the serious traveler. Their classifieds in particular are quite helpful,
Palio information - The official Siena Palio site.
Siena Jazz information - In Italian only this is a great place to learn about the jazz music program and concerts in Siena.
Siena news -- One of the best sites for updated information and news on, about and from Siena, in Italian only. Links in the right hand column will take you to the official sites for the Commune, the Provincia (province) and Preffetura as well as the APT site.
Sienaol.it -- in Italian and English this site is not terribly well-designed but does have some potentially valuable information on the splash page; they do list the winner of the latest Palio right up front which is nice. More. . .
Sienaweb -- A collection of links to various online resources covering a variety of diverse topics: astrology, go-kart racing, tourist accommodations, etc. In a combination of Italian and English.
Siena turismo -- In Italian only but has a wealth of local tourist information.
SlowTrav Italy -- One of the best online resources for finding information quickly and easily; with great navigation and very user friendly interface. Solid information, based largely on the reports of intelligent and lucid travelers themselves, outstanding reviews and very consumer oriented.
Weather in Siena - from Weather.com

For accommodations:

Click here to search for a hotel in Siena or Tuscany (and help keep this site active)

Alteernatively, if you're looking for vacation rentals we have often used one of these following sources:

Caffeletto
Initaly
Italianvillas.com
Karen Brown
Rick Steves
The Parker Company

For transportation information:

Autostrade - For up-to-the-minute information on the toll highway system.
Touring Club Italiano - Italy's version of the North America's AAA club
RenaultUSA - You get a brand-new car, fully insured, zero deductible (very important) for a lot less than you would spend on a typical rental car.
InItaly Transport Links - Source for a wide variety of transportation information; particularly helpful for tracking down ferry information.
The official Italian railway website is a breeze to use and very easy to understand (it is in English as well as Italian). Additional train information can be found at Turismoverde.com.
Bus from Rome to Siena -- This is the site for the "Sena" (not Siena) bus line which services the Siena to Rome route.
Bus from Siena to Firenze -- This bus schedule is found at Turismoverde's website as is a handy train schedule (see above).
Local bus -- Called "TraIn" -- confusing I know -- the orange buses service nearly every community in and around Siena. Their main office is underground at the Piazza Gramsci. You can find the entrance right in front of the Jolly Hotel. Weekly and monthly passes are available.

If you are looking for information on moving to Italy check out some of the sites we have come across, just click here