Ones not mentioned that are good.
Birth of a nation 1915 (American, silent) long as shit though.
Das Kabinett Des Doktor Caligari 1919, (aka cabinet of Dr. Caligari, European, Silent) Tim Burton must have been inspired by this one.
Broken Blossoms 1919 (American, silent) depressing but good.
All Quiet On The Western Front1930 (American) classic
City Lights1931 (American, Silent) Charlie Chaplin epic.
Freaks 1932 (America) horror using real circus freaks.
Triumph Des Willens 1934 (aka Triumph of the Will, European) Excellent documentary on Hitler while he was alive, this one really shows you a different side of the nazis as more of a politcal party than video game bad guy clichés.
The Maltese Falcon 1941 (American) Film noir they way its supposed to be done.