You should take a look at the Radical Reference Reference Shelf page on History, Resistance for some good alternative sources/collections.

For books, one place to start would be Philip S. Foner's masterful History of the Labor Movement in the United States, especially volumes 3-10, and other works by this labor historian. His nephew, Eric Foner, is also an historian worth reading - though his area is mostly 19th century, a list of his books reveals some good titles for the 20th which you can find in your local library. While we're at it, Nancy Foner (I'm not sure of the relation, if there is one) is a sociologist who has written extensively on immigration.

I would certainly recommend a look through some works by Howard Zinn, especially (for an overview) A People's History of the United States, which though written for a popular audience would provide you with further citations to follow up on.

For the South, check out Defying Dixie : the radical roots of civil rights, 1919-1950.

This is just a starting point; I hope we will continue to add to the list. Also, once you have any of these books, especially more recent ones, check out the bibliography/reference list for further reading.