Classified: How to Stop Hiding Your Privilege and Use It for Social Change!
Karen Pittelman and Resource Generation, Illustrated by Molly Hein
http://www.classifiedbook.com/downloads.html <-- you can download the ENTIRE BOOK here.
This handy text focuses on issues of class. The first few chapters discuss the way class "hides" through code words, issues of hidden privilege, and fear of being marked as the "oppressor." The later chapters move towards a more agency-driven analysis -- they discuss how one can use one's class privilege to act as an advocate for social justice.
Using comics, activites, and confessions, Classified is both a great resource on class and a useful way to model what being a good ally "looks like."