All Quiet on the Western Front (1930): Classic, powerful anti-war movie depicting the horror of WWI-era trench warfare from the viewpoint of a young German enlistee.
Z (1969): A great political thriller about the assassination of a popular Greek leftist politician by the military establishment. Based on a real incident.
12 Angry Men (with Henry Fonda) (1957): The movie chronicles a jury deliberation in a murder trial and shows how different life experiences can impact jury deliberations in very real ways. The wonderful cast breathes life into the twelve very different men. Henry Fonda is the thoughtful, darn likable protagonist. The recent remake is ok but inferior to the original.
Little Big Man (with Dustin Hoffman) (1970): A 121-year-old man claims to be the only survivor of Custer’s Last Stand. Hoffman plays the man from a teenager adopted into a plains Indian tribe to the ancient embellisher. Very entertaining, and, simultaneously, a fairly effective depiction of the tragic treatment of Native Americans in the 19th Century.
Lenny (1974): Dustin Hoffman as 50s vulgar, provocative comedian Lenny Bruce. Need I say more?