Thinking outside the box:
http://www.greencarcongress.com/2009/03/lightning-hybri.html#more

Good luck to them but my question to them is: how do I recharge so I will not use any fuel? Also:

"Lightning Hybrids is keeping specific design details secret, pending US and international patent filings. The company says it anticipates numerous patent filings, the most significant attributable to the design of an integrated hydraulic axial piston engine. Claimed features of the drivetrain include:
* Lightweight; <1 lb/hp
* true cylinder deactivation for high part load efficiency
* no transmission
* no valves, flywheel or crankshaft weights
* 100% energy braking recovery

100% energy recovery???

We are going to see how drastically prices will drop in hybrid designs that forego any batteries. Right now, it's hydraulic systems. In the future, it may be capacitors.

100% energy recovery???

100% is a dumb claim, we all know that is not possible, however I think that near 90% is. I know nothing about this company or what it claims it has patents on, but I do have an idea as to what they are up to. It is a parallel hybrid like the Prius, but the difference is the engine is a two stroke diesel with cylinder deactivation, no big deal here and a hydraulic motor with a gas storage chamber.

When the brakes are applied, the hydraulic motor compresses an inert gas in a sealed chamber, probably Nitrogen and a valve/regulator keeps the energy in. Then when you step on the gas, the valve opens and the gas expands powering the hydraulic motor that assists the diesel engine. It is a closed system, so the hydraulic fluid and the Nitrogen gas never goes anywhere, it just gets pushed back and forth. Not a bad idea, but fraught with engineering challenges. Hydro-pneumatic power storage, two stroke diesels and cylinder deactivation have been around for decades, it's the coupling of technologies and putting them to work in a car that is a challenge. However this energy capture system combined with a high tech diesel engine could very well get to 100mpg.