[ejguillot]

There is: The mild hybrids that GM is cranking out do exactly that. An oversized alternator and battery pack that can drive most accessories by electricity (power steering, AC, and so on) so that the engine can be stopped while you wait at a traffic light and the AC keeps you cool. Step on the gas and the engine restarts instantly.

GM should find the money to make this standard on every vehicle they sell.
Wish mine had that, city gas mileage sucks on mine as bad as a current gen STS.