I spent some time at my brother-in-laws thinking about this topic. Similar to how we listed our favorite cars, I broke my list into eras. Because of the often flexible use of the word sedan, I will include proper 4-seat 2-doors as well as 4-door cars.
1940-1970: VW Beetle - This car made everyone question the conventional wisdom of cars.
1950’s: 1956 Fords. This was the first time a major US producer offered safety features like padded dash, and seat-belts. It was a total flop, but showed that safety didn’t need to break the bank.
1960’s: Chevy Corvair. The Corvair is on my list for the same reason as the Beetle. It was a bold move on Chevy’s part to make mix a rear engined car with American styling.
Unfortunately, Chevy decided to introduce the car with swing arm suspension in the rear. Ralph Nader’s book, Unsafe at Any Speed, pointed this decision out (and was equally as critical of VW’s same decision on the Beetle, although only people who read the book would know…). By 1965, Chevy had perfected the car with a new independent rear suspension design, but the media buzz around Nader’s book killed the product line.
Ironically, it’s death maybe the most important thing about the Corvair sedan. The issues of safety raised by it have been affecting legislation and buying habits of consumers since.
1960’s: Citroen DS. This car blew off every traditional styling trait. The engineering was as pretty as its lines too. It’s a pity no automaker has the balls of Andre Citroen today.
1970’s: BMW 2002 and 1600. These cars are significant because of their early adopter status. The buyers of these successful designs drove later buyers from the traditional US luxury brands, like Cadillac, Buick, Lincoln and Chrysler, to German brands.
1980’s: Design wise, the Honda Accord and Toyota Camry were , at best, boring. However, they intorduced American car buyers to the concept of “reliability”.
1990’s: Ford Taurus. Ford broke away from the box with the Taurus, and was awarded with great sales. It’s hard to believe the big 3 could run with Camry and Accord as late as the 1990’s, but that’s what Taurus did. It’s a pity Ford dropped the ball with the second generation, sales plummeted.
2000’s: Ford Focus. Focus broke away from the formless blobs of cars like the Taurus II and Eclipse II. Looking back, it really seems like Edge styling was the car that broke the styling ice. It feels like ever since, makers are a little more free to be different…just a little.
2000’s: VW Golf. VW showed everyone that style pays again. They took an unreliable and ancient engineering platform and made is shine like gold. Brillant!