Mercedes-Benz S350 Bluetec 4Matic (US)
This generation of the Mercedes-Benz S550 (chassis W221) launched in the US with two models - the mainline S550 and the super-expensive S600. Eventually other models were added, including the S400 Hybrid and the S350 Bluetec; both models cost a bit less than the S550 while delivering better fuel economy.
The S350 Bluetec is part of a new generation of clean-diesel German cars meeting California's stringent emissions regulations. These German cars use AdBlue, a proprietary urea solution, to reduce the nitrogen oxide emissions; AdBlue is slowly used up over time, so it needs to be refilled once a year. These vehicles also need the low-sulfur diesel fuel that is common in Europe but was unavailable in the US until 2007 or so.
In the US, diesel-powered cars have limited appeal, partly because only selected gas stations have diesel, partly because diesel fuel often costs much more than gasoline (wiping out the diesel fuel economy advantage), and partly because the late 1970s General Motors diesels, hastily converted from gasoline power and notorious for engine failures, had left a bad taste in the motorists' minds.
In any trim, the W221 is one car that is always sentimental to me; it is the only model for which I have been able to see the final assembly process in person. My 2009 tour of the Sindelfingen factory (part of my W212 E-class European Delivery) included a tour of the S-class final assembly line, and I remember the cars going from an empty shell to a fully alive machine in a step-by-step manner. This example, like all other US-market S-classes, came from the very Sindelfingen assembly line I had toured.
Seen at Los Angeles International Auto Show, 2011.