The Legal Information Institute of Cornell University Law School hosts the Congressional Research Service's Annotated Constitution, a highly useful source for studying the Constitution. An entire section is devoted to the Fourteenth Amendment, with a subsection dedicated to the equal protection clause.
Oyez, a searchable database of United States Supreme Court cases, is an excellent source for studying American legal history. The site provides efficient case summaries, audio files of the oral arguments, and links to written opinions.
The Library of Congress has created a web guide for the Fourteenth Amendment that includes historical documents, links to useful cites, and a selected bibliography.