Perhaps the easiest way to make a car more fuel-efficient is to make it lighter. The designers of the Edison2 concept vehicle have taken auto dieting to the extreme. The car as aerodynamic as it is anorexic weighs less than 800 lb., which helps it get 102.5 m.p.g. That was good enough to share the Progressive Insurance Automotive X-Prize, an award set up to encourage development of production-ready cars that are super-fuel-efficient. Sadly, Edison2 team owner Oliver Kuttner says you won't see the car at your dealer anytime soon. But it's a hopeful sign for an oil-pinched future.