A British group named Foresight Vehicle
Visteon UK Ltd has created a device called TIGERS (Turbo-generator Integrated Gas Energy Recovery System). It uses the exhaust gas from a car's combustion engine to produce electricity, enough to power the vehicle's electrical system, thus taking a load off the engine; "Parasitic losses from mechanical support systems (i.e., belt-driven) can normally be as high as 6kW or 8hp in a family sedan but can be significantly higher in larger capacity cars and trucks. Moving from those mechanical systems to electrical removes those loses, and fuel consumption could be reduced from between 5%–10%
." This technology could be coupled with hybrid technology and the extra electricity could help recharge the hybrid's batteries. "Because the system is fairly simple and partly based on existing technology, it could be fully developed for all car, van, bus and truck engines within a few years." Now lets wait for a successful mainstream implementation. Much more details available at the two links below.
Update: Thank you Chris Stevenson for correcting some errors in this post.
::Foresight Vehicle, via ::Green Car Congress