It is true that diesels produce less CO2 but the NO2 and the particulate matter is still very high on the "cleanest" of diesels sold here in the states. European gas is actually of lower quality because they have fewer controls on it than in the US. BMW and Benz have made a committment to making cleaner diesel engines and they have started to mate them to hybrids. Still by far the Prius is the best choice for the enviroment, fuel economy, and the PRICE! If you are not hurting for a car now, i would wait on the prius. It will become more avalible and you will be glad you waited.
The best US available "modern" diesel I know of is the 300E Benz Turbodiesel, last offered in 1999. They are again available as, I think, an 04 or an 05 in states where low-sulfur diesel is available (alas, not in MA I had one, and they are truly remarkable in terms of torque and mileage, but the particulate emissions is what I did not want... Peace
