Hi
I am planning a trip for Florence and Siena in early August.. first week in Florence and the 2nd in Siena ..to catch the festivities of the Palio.
Might you have any suggestions on reasonable accommodations ( in a central area) in both Florence and Siena?

You need to give a price range.

Though I think they're unlikely to have availability on such short notice, this is a very nice place in Florence:
Residenza Il Villino
http://www.ilvillino.it/home.cfm
Lovely rooms and the hosts are terrific.
And they offer special weekly rates.
I haven't stayed in summer, but the website says they have A/C (double check that). It's about 2 blocks from the center.
Good luck!

I stayed at www.sanlorenzohotel.it
it was safe, clean and breakfast was included.
I loved the location too...

Florence-

http://www.ilsalottodifirenze.it/en/index.php
http://www.florencegrandtour.com/index.php
http://www.proconsolo.com/
http://www.sanlorenzohotel.it/rooms.php
http://www.hotelsantacroce.it/20,20.html
http://www.hotelbalcony.com/en/rooms.htm
http://www.hotelcestelli.com/
http://www.hotelporcellino.eu/
http://www.touristhouseghiberti.com/eng/01-home.html

Florence apartment-
http://www.residenzailcarmine.com/


Siena-
http://www.residenzadepoca.it/index.php