If you have an extra money lying around and would like to plug 'n play your car then you'll love what the researchers have done to a Toyota Prius. According to The Rocky Mountain News, The Renewable Energy Laboratory folks in Golden Colorado have placed a solar panel on top of the Prius and put an extra large lithium-ion battery in the trunk.
After testing, the car got approx. 100 mpg for the first 60 miles without a gas engine. The car can conveniently be charged by connecting it to a normal household or business electrical outlet.
Bad news is that the car is $40K, the panel is $2500 and after they installed all the bells and whistles on it the price shot up to $70K. But, it's only a research model and nowhere near ready for retail.
It will probably be years before Detroit gets ready to market something like this at affordable price. But there are individuals who have already experimented with this technology. If you go to the "Solar Vehicle" section of Solar Power Videos you'll see examples of guys who have been experimenting with creating solar powered cars:
Solar Power Videos