For those of you in the Southern California area, the Izod Indy Car Series will be having a test day in Fontana on Tuesday, September 24. The event is free to the public and if you are going to the race in October they are holding a Q&A session with the drivers, too. That should be good for some nice candid portraits.
http://www.autoclubspeedway.com/Tickets-Events/Events/INDYCAR-Weekend/INDYCAR-Test.aspx
http://www.autoclubspeedway.com/Tickets-Events/Events/INDYCAR-Weekend/INDYCAR-Test.aspx