Primary Source Explorer: Martin Luther King, Jr. and Cesar Chavez
The Martin Luther King, Jr. Papers Project
http://www.stanford.edu/ group/ King/
This site from Stanford University is a good starting point for researching the life of Dr. Martin Luther King, Jr. In addition to a thorough biography, you'll find many articles about King and primary-source documents, including King's "I Have a Dream" speech from the March on Washington in the summer of 1963.
The Greensboro Sit-Ins: Launch of a Civil Rights Movement
From the Greensboro Public Library and the Greensboro News & Record, this Web site is an outstanding resource for learning about the Greensboro sit-ins of 1960. The incident that sparked the sit-ins is documented in a series of audio clips. You can download firsthand accounts from the people who experienced this part of history, including the four African-American college students and the manager of the store that refused to serve them.
The United Farm Workers: History
Find information about the history of the United Farm Workers (UFW) and Cesar Chavez on the official site for the UFW. Check out the biography of Chavez, a chronology, and the text of some of Chavez's speeches.