The Very Big, Very Green Mercedes....

The 2010 S400 Hybrid is the world's first production car with lithium-ion battery technology and as you'd expect from the bright boys in Stuttgart, it's a marvel of creative engineering.
Once you admit that rich guys crave big, luxurious wheels no matter how much they profess to care about the ecological health of our planet, the smart move is to give them what they want. Design a land yacht with low emissions and reasonably good gas mileage that's wrapped in soft leather and kitted out with every imaginable high-tech gewgaw and you'll have a car that makes your customer feel good while he's flaunting it.
The trickiest bit on the S400 is the engine, which shuts itself off below 9 MPH and quietly revs itself up again when you step on the gas, thereby saving the fuel that would be wasted while standing at red lights and such. That makes for fuel economy of 20% plus lower emissions over the standard S550 which averages 15/23 MPG as opposed to the S400's 19/26 MPG.
There is of course, a trade-off: a loss of power from the revised V-6 engine that pushes out 295 HP as opposed to the 382 HP V-8 of the S550 but there's also a bonus that covers the loss. No gas-guzzler tax, an entry price of $87,950 rather than the usual S-Class $91,600 and a $1,150 tax credit for going green. Not a bad deal at all.