Class Action is a non-profit that offers training and consulting about the issues of class and money, and their impact on our individual lives, our relationships, organizations, institutions, and culture.
Class Matters offers information on cross-class organizing, how class intersects with other identities, and various ways of defining and understanding class (in US society). They also have a wonderful page called "Tips from Working-Class Activists."
The Center for Working Class Studies at Youngstown State University has resources including famous working-class literature (think William Faulkner), a "Working Class Perspectives" blog, and an ethnic community archive of Mahoning Valley (where Youngstown is located).
The Center for the Study of Working-Class Life at the State University of New York — Stony Brook has biannual "How Class Works" conferences (in June of even years), as well as resources for learning more about labor issues or to get help in organizing for economic justice.
Resource Generation works with young people with financial wealth who are supporting and challenging each other to effect progressive social change through the creative, responsible and strategic use of financial and other resources. As well as online resources and organizing, there are local chapters in Philadelphia and many other major US cities.