The Wikipedia entry for caste provides a good starting point for people to explore the issue of caste. It provides a historical overview, the modern status of the caste system, the caste system among non-Hindus in India as well as sections on caste politics and caste related violence.
This easy to read overview of the caste system was produced by the Federal Research Division of the Library of Congress as part of their country studies and funded by the US Department of army. It gives the reader with little background of the caste system the basic history and general features.
An audio on the Human Rights interviews Smita Narula, faculty director of the Centre for Human Rights and Global Justice who offers a pessimistic account of caste in modern India.

The Dalit Freedom Network’s mission is to empower Dalits to obtain social freedom and human dignity. As well as information about the network, this website provides background as to who Dalits are, and their position in the caste system.