Kanopy - thousands of classic feature films, educational shorts and documentaries. Try starting with Race & Class Studies or Media Studies.
Docuseek - a collection of documentaries and educational films geared toward a wide range of disciplines, including Communication and Media Studies.
MEF Digital - a collection of films that inspire critical reflection on the impact of American mass media. Includes Killing Us Softly and special collections examining gender and race in the media.
Filmmakers Library Online - a small collection of documentaries dealing with a wide range of social, historical issues & cultures; try exploring the films under the Diversity subject.
Film Platform - a collection of cutting-edge documentaries from around the world, covering a wide range of topics
Can't find the film you're looking for at the MDC? Here are some sites that might offer it free or for a fee: