What doesn't the Standford History Education Group have on their site? The site offers everything from lesson plans, to primary source materials, to pedagogical approaches to teaching history, to assessment materials. This site has especially great tools for getting students to think like historians!
The American Civil Liberties Union has a vast array of materials hosted on their site. Perhaps the materials of greatest use to teachers are the frequent "news releases" about issues pertaining to our individual freedoms that are currently in the news.
The Bill of Rights institute offers a wealth of materials for teachers. In addition to copies of each of the Founding Documents and accompanying essays about each, there are many other materials on the site. Among my favorite resources are the many lesson plans made for teachers of all levels.
The Oyez Project is the best site available for Supreme Court decisions and business currently before the court. As I write this description, there are currently two articles about the court considering same-sex marriage issues on the front page.
This is the National Archives' "Charters of Freedom" website. In addition to having full transcriptions of the DOI, Constitution, and Bill of Rights, there are links to many ancillary materials as well. Included in the site are lesson suggestions, other primary source materials, and scholarly essays about the legacy of our Founding Documents.
This is a link to the Bill of Rights Institute's page concerning the Equal Protection clause of the 14th Amendment. The page includes links to primary source materials and summaries related to important 14th Amendment precedents (Plessy, Brown, Korematsu, Loving, Bakke, etc).
This is link to a PBS website called "The Rise and Fall of Jim Crow". This particular page explores the ratification of the 14th Amendment. It also includes links to short videos and related documents.
This is a link to the 14th Amendment on the Library of Congress website. There are also links to additional primary sources related to the 14th Amendment on this page.