Nice Ecomodding Summary with reference to Ecomodder!
 

Found this nice source of both passenger car aerodynamics and eco-modding summary (with reference back to ecomodder!):

The Recumbent Bicycle and Human Powered Vehicle Information Center

They say to install a cold air intake, a mod that has been shown to reduce MPG on gasoline powered vehicles.
Also to install a high flow air filter, a mod that has been shown to be a waste of money on gasoline powered cars.
And to remove side mirrors, and replace with cameras something that will surely get you pulled over, at least anywhere on the east coast and ticked.