Dziga Vertov's 1929 Soviet city-symphony. The Sight & Sound poll's #1 documentary of all time. A still-radical experiment in pure cinema.
From Wikipedia
Man with a Movie Camera is a 1929 Soviet experimental silent documentary film, written and directed by Dziga Vertov. It was filmed by his brother Mikhail Kaufman, and edited by Vertov's wife Yelizaveta Svilova.