I am a big fan of what's been mentioned here already - Big-fin Caddy's, Oldsmobiles, etc from the 50s/60s/70s. You guys know I love my land yachts.
A classic car that I feel is constantly overlooked from a styling perspective is the Nash Ambassador, especially the 1949-1951s. I just love the hidden wheels and upside-down bathtub body design. Combined with '40s-50s engineering and interiors, and you get a very unique look. I love the simple, streamlined rearend, too.
http://www.collectorcarads.com/Picture1/1949nashsuper_1.jpg
I'm also a big fan of CORVAIRS, especially 2-door hardtops. Nothing to me combined styling elements of the '60s sports cars better than the '65-69 Corvair 2- and 4-door. No B-pillars!!! Considering how they developed a wagon, coupe, sedan, minivan, and pickup...there were properly legitimate plans to take the success of the air-cooled VW Beetle and make a whole future for GM out of it. I appreciate that the engineering was so strong around air-cooled cars for daily drivers.
http://www.thetruthaboutcars.com/wp-content/uploads/2010/04/CC-58-019-800.jpg
As I get older, simple car designs and engineering appeal to me a lot more than the complexities mandated by governments these days. Still some great cars, but in terms of the classics, these do it for me.