These guys have an interesting product in development. It's a hybrid kit that turns nearly any car into a battery/electric motor assisted hybrid. Mileage is supposed to nearly double using the kit. According to the designer, if you can change your brakes, you should be able to install the kit. They are hoping to sell it to car manufacturers as a dealer installed option.
The Kit That Turns Any Car Into A Hybrid | This Could Be Big - Yahoo! News
The Kit That Turns Any Car Into A Hybrid | This Could Be Big - Yahoo! News