History is a Weapon is a broad collection of essays on social change from a variety of political tendencies. Sections include "What is this America?" and "From Resistance to Revolution".
Revolution in the Air is a website with resources related to the book by the same name by Max Elbaum, which is a look at the birth of what he terms the New Communist Movement[s] of the late 1960s. History and Strategy section includes a political chronology from 1954-1992.
The NameBase Directory is an index of people influential in politics, the military, intelligence, crime, business, and the media since WWII. It started in the late 1960's when New Left activist Daniel Brandt began clipping magazine and newspaper articles and collecting investigative books about the power structure. He combed each book and article for the names of individuals, groups, corporations, and countries - developing a name authority file along the way. In the early 1980's, he incorporated Public Information Research to continue the work. NameBase includes close to 100,000 names from approximately 260,000 citations. The names are drawn from over 700 books and serials, plus a handful of documents recovered using the Freedom of Information Act (FOIA). While the index does draw from the mainstream and right wing press, most books and articles come from a leftist perspective. (description from http://www.bowdoin.edu/~samato/IRA/reviews/issues/oct00/namebase.html) Sections include information on the CIA and foreign policy.
Marxists Internet Archive is a huge resource of essays by Marxists like Lenin and Mao, as well as non-canonical people like Gramsci. There are also resources on Malcolm X, and the anarchists Bakunin, Emma Goldman, and Proudhon.
The Labadie Collection at the University of Michigan has been digitizing anarchist pamphlets that were once held by anarchist Jo Labadie. There are also feminist and queer liberation materials.
Anarchy Archives is an online research center on the history and theory of anarchism.
The Southern California Library is a collection of materials focusing on the Left history of Los Angeles, with other general materials on social-justice struggles from around the U.S. and the world.
Lesbian Herstory Archives, the largest and oldest Lesbian archive in the world, began in 1973 as an outgrowth of a Lesbian consciousness-raising group at the Gay Academic Union. The founders were concerned about the failure of mainstream publishers, libraries, archives, and research institutions to value Lesbian culture. It became obvious that the only way to insure the preservation of Lesbian culture and history was to establish an independent archives governed by Lesbians.
The Chicago Women's Liberation Union has a website with an archive of articles on topics like: consciousness, family, sexuality, and internationalism. They also have a number of articles from the publication Womankind.
A number of issues of the Left journal Radical America have been digitized by Brown University. Part of what Max Elbaum considers the New Communist Movement, Radical America has articles from some great theorists. Radical America ran from 1967-1999 (with much fewer issues at the end).
Freedom Archives is based in San Francisco, and is a great resource for finding audio on social movements. According to their website: "8000 hours of audio and video recordings documenting social justice movements locally, nationally, and internationally from the 1960s to the present. The Archives features speeches of movement leaders and community activists, protests and demonstrations, cultural currents of rebellion and resistance."
African Activist Archive "is preserving records and memories of activism in the United States to support the struggles of African peoples against colonialism, apartheid, and social injustice from the 1950s through the 1990s."