Stanford University has created a nice website for learning about Martin Luther King and the legacy of his struggle to advance civil rights in America.
At their website The Martin Luther King, Jr., Research and Education Institute look for the Quick Links option of "Teaching King."
From there you can find lesson plans, primary and secondary sources online, classroom resources, an encyclopedia and more.
The Library of Congress also has an amazing set of links to source materials for teaching about the American Civil Rights Movement.
