Diesels are fuel efficient and practical, but they're dogged by a reputation for being about as much fun as a tax audit. VW's worked hard to change that perception with cars like the Jetta TDI, but it might be the sweet Concept BlueSport roadster that finally convinces Americans diesels are cool. The mid-engined sports car made its world debut at the Detroit auto show, and although it's just a concept, there's no reason why VW couldn't - or shouldn't - build it. The car gets 42 mpg and emits about as much CO2 as a Toyota Prius, and it is emissions-legal in all 50 states so even car-crazy Californians could buy one.