While many books and essays discuss class, I have found these to work well for my students. They are readable, reasonably clear, and of manageable length for advanced undergraduates and graduate students at a largely working-class university. - Sherry Linkon
Patrick Joyce, ed. Class, Oxford University Press, 1995.
A collection of excerpts from a wide range of theoretical discussions of class, from Marx and Engels through contemporary critics.
Jack Metzgar, "Politics & the American Class Vernacular," in New Working-Class Studies, Sherry Lee Linkon and John Russo, eds. Cornell University Press, 2006.
Connects ideas about class to recent politics and the ways that the media typically talks about class. Provides a useful introduction to the idea of class as culture.
Raymond Williams, Keywords: A Vocabulary of Culture and Society, Oxford University Press, 1976.
The section on class offers a useful overview of approaches to class, with lots of references.
Erik Olin Wright, Class Counts, Cambridge University Press, 2000.
Provides a very readable overview of ideas about class structure and class formation.
Michael Zweig, The Working Class Majority: America's Best Kept Secret, Cornell University Press, 2000.
Offers a clear, contemporary overview of a Marxist approach to class.