Battleship Potemkin (Silent - 1925)
Director: Sergei M. Eisenstein
Plot: A dramatized account of a great Russian naval mutiny and a resulting street demonstration which brought on a police massacre. With workers striking in Russia, the crew of the battleship Potemkin feel a certain kinship for the plight of their brothers. When they are served rotting, maggot-infested meat, some of the crew object only to find themselves singled out and placed in front of a firing squad. With the marines seconds away from firing the deadly shots, ordinary seaman Vakulinchuk steps into the breach and intervenes to save the men by appealing to the firing squad to ignore their orders. When the officers take their revenge, all are bonded together in the struggle; a bond that reaches to the city of Odessa where the rebellion grows, leading to a bloody and historic series of events.
Quite a lot has been said about this film and its landmark importance in forming the language of film. If you are interested in film history, to truly understand the innovations Eisenstein brings to the medium you might try viewing Potemkin along side most any film made before it (those of D.W. Griffith offer a good contrast). It should be allowed that Eisenstein was not the only montage theorist and the principles of montage editing would likely have been discovered by another given time. However, even today, few directors have approached the skill with which Eisenstein created meaning through the combination of images at such an early point in the evolution of the medium.
If you are not interested in that sort of thing, Potemkin is still one of the most beautiful and moving films ever made.