The VW and Benz vehicles, Automotive News reports, both fall under the new federal alternative-powertrain tax credit. The Benz SUV lineup gets credit for its new diesels, from a $900 credit for the ML 320 Bluetec (shown here) to $1,800 for the GL 320 diesel.
The News doesn't mention the E320 Bluetec sedan, but does say the credits are based on how much fuel these new diesel models save, versus similar models on sale in 2002.
Only 60,000 tax credits per carmaker are available, so it pays to be an early adopter here. The Benz diesels go on sale in October.