This is an old idea who's time may have finally come. Brian Wang has written a great post over at Next Big Future about flying cars. His idea is that small electric airplanes could be incredibly efficient - 438 MPG equivalent.

Of course one big problem with flying cars has always been that airplanes are much more difficult to pilot than cars. Brian argues that UAV's are proving that robotic flying could be very safe. It would be push button flying. It wouldn't be any more difficult than using a GPS. You tell the aircraft where you want to go and it does the rest. It plans the flight (including determining whether fuel stops will be necessary), files a flight plan, communicates with ground control, taxis to the runway, takes off, stays in contact with aircraft control, and lands - all on its own. The driver could always change the destination en route if desired, but the aircraft itself does all the flying.

When you get to your destination airport you detach the flying chassis and drive away. I would guess that the upper flying chassis would probably be powered by liquid fuel while the car could be powered by batteries (but see Brian Wang's post on electric aircraft). These flying chassis could be interchangeable. They would be kept and serviced at the airport. You'd rent them as needed.

So, what production car would be good for flying? Jesse James used this sports car:

But this thing flew only 300 feet or so (video link). It was more like an Evel Knievel stunt than flying. There are probably better, lighter cars that would be more practical. Something like this:

This is the Aptera Type 1. It will come in two models - all electric car and hybrid. The all electric will have a 120 mile range. The hybrid is said to get 300 mpg with an increased range. The top speed of both models is 90 mph. Here's the Popular Mechanics story on the car:

This is another way that the electric cars could become practical long-range vehicle. For short trips you drive. For long trips you fly. If there's sufficient gas in reserve, the flying chassis could even charge your battery as you go. It could even become a popular alternative to commercial flying.