First the protest/union hall set, these folks travel the radical circuit (playing mostly non-profit venues, fundraisers, protests, rallies, etc). Their music is overtly radical and can range from brilliantly revolutionary to hokey preaching to the choir depending on your mood.
David Rovics - Sings Woody Guthrie style folk tunes about contemporary radical issues. Unions, Indymedia, Anti-Free Trade protests, direct action, anarchism, etc.
Charlie King and Karen Brandow - Charlie has been doing radical folk music since the 70s. Anti-war, pacifist, labor stuff.
Anne Feeney and Chris Chandler - Chris is a street poet from Philly and Anne has been a Labor Troubador for a few decades. Alone they are each awesome but together they're even more powerful. Chris does spoken word interludes over Anne's songs, they trade back and forth between singing and poetry every verse. So it's like the overlap of a poem and song about two different related things. Very cool stuff.
Jolie Rickman - Punchy Anarcho-feminist eco-folk. AWESOME stuff.
The next batch are more likely to be found playing the folk music circuit rather than the radical circuit but they are no less radical in their music. Alix Olson, Pamela Means, and Doria Roberts often coordinate their tours and guest appear at each other's shows.
Pamela Means - Very fast VERY high energy urban feminist folk. Race, gender, queer conscious.
Doria Roberts - Everything I said about Pamela, I say it about Doria. Not as fast, more melodic singing. AWESOME. A REALLY nice person to work with.
Alix Olson - Queer Feminist slam/performance poet. If you like Ani's poetry, you'll love Alix.
Allette Brooks - Eco-folk but much less agressively political than the other artists on this list. The personal is political and her politics weave through her folk songs, she's very socially conscious but many of her songs are love songs and other traditional non-overtly political folky fair. She's got the West Coast (San Fransisco) style whereas most of the others on the list are East Coast (Boston/New York).
Matewan - Completely brilliant! About miners in Virginia struggling to build a union around the turn of the century. Covers the interelations of labor, race, religion, immigration, class, private/public power, culture, etc that all ring true today. The central character is inspired by Joe Hill the famous IWW organizer. Directed by John Sayles, my favorite all time director. Any of his movies would be suitable for your list as they all deal with race, culture, and/or community. (****)
Bullworth - What if a politician had nothing to lose and told the truth? Comedy. Hilarious. (****)
Woodstock - Amazingly filmed vision of 3 days of peace and love. Covers the successes and the failures, the good and the bad, of this one (accidental) amazing utopian moment in the 60s. (****)
The Thin Blue Line - An chilling anti-death penalty movie by the master of documentaries, Errol Morris. (****)
Silkwood - The story of Karen Silkwood, a nuclear power whistle blower who was murdered for her activism. (***)
Steal This Movie - About Abbie Hoffman's anti-war activism in the late 60s and the FBI's COINTELPRO efforts to silence and discredit him. (***)
Panther - about the Black Panther Party for Self Defense (**)
Incident at Ogala - About the shooting at Pine Ridge Reservation which American Indian Movement leader Leonard Peltier is in jail for life for. (**)
Reds - About american radicals around the time of the 1917 Russian Revolution. (***)
China Syndrom - Fictional anti-nuclear movie inspired by the Three Mile Island incident. (**)
Norma Rae - A single working mother helps unionize textile workers in the 70s. (***)
The Hurricane - The story of Rubin "Hurricane" Carter, (subject of a Bob Dylan song) a boxer wrongly imprisoned for murder, and the people who aided in his fight to prove his innocence.