The classic era of American automobile design began in the 1920s and lasted through the late 1930s. Here are some of my favorites:
1927 Kissel 8-75 Speedster
1929 Jordan Speedboy G
1929 Duesenberg J 350 Willoughby
1930 Pierce Arrow Roadster
1932 Cadillac 355B Sport Phaeton
1932 Pierce Arrow Model 54 7-Passenger Touring Car
1934 Packard Eleventh Series Eight 1101 Convertible Sedan
1935 Auburn 8-851 Cabriolet
1937 Cord Model 812C Phaeton
1938 Lincoln Zephyr Convertible Coupe
Many collections of classic-car photos and specs are available online. Conceptcarz.com is the best that I have found. The collection there spans the late 1800s to the present. See also the excellent Crawford Collection of the Western Reserve Historical Society.