Here is a digital archive devoted to writings of Dr. Martin Luther king jr. at the Martin Luther King Jr. Center for Nonviolent Social Change.
Mahatma Gandhi.org includes writings, quotes, philosophy, timelines, photos, and much more about Gandhi.
Malcolm X.org has a list of documents that you can view, including interviews and letters.
For a pdf viewing of Franz Fannon's The Wretched of the Earth, click here.
Also by Fannon, Black Skin, White Mask can be viewed as a pdf here.