It's called The People Speak, a documentary based on Howard Zinn's groundbreaking books, A People's History of the United States and Voices of a People's History of the United States. both books I STRONGLY recommend, it you haven't already read them - notably the former, which I've committed to re-reading once every year!
The film brings together accomplished performers to re-create the emotional impact of moments in American history - several great speeches from the voices of those marginalized, rarely heard in mainstream histories, like Malcolm X, Abbie Hoffman, César Chávez, Frederick Douglass, Sojourner Truth, Allen Ginsberg, and countless others.
These readings are woven together with historical footage, music and narrations from Ben Affleck and Howard Zinn.
Featured appearances include: Don Cheadle as Richard Wright, Danny Glover as Frederick Douglass, John Legend as Muhammad Ali, Mos Def as Malcolm X, Kerry Washington as Sojourner Truth, Jasmine Guy as Abbey Lincoln, and Michael Ealy as Benjamin Banneker, and many, many more... Viggo Mortensen, Sandra Oh, Sean Penn, Rosario Dawson, Matt Damon...
The program will air in TV and be released on a special DVD some time next year. I have no idea when exactly, and couldn't find any more info.
Now that it's on my radar, I'll certainly be looking out for it. You can sign up for future updates at the film's official website: http://www.thepeoplespeak.com/.
Here's the trailer: