A Century of Lawmaking for a New Nation: U.S. Congressional Documents and Debates, 1774-1873
http://memory.loc.gov/ammem/amlaw/ 
From the Library of Congress, a site containing archived primary source documents of Congressional publications from the first 100 years. The site offers congressional journals, delegates' letters, floor debates, bills, resolutions, and statutes. These documents can be browsed by Congress and/or searched by keyword. 

Constitution of the United States of America: Analysis and Interpretation 
http://www.gpoaccess.gov/constitution/browse.html 
From the Congressional Research Service, Library of Congress.  An annotated text, incorporating Supreme Court decisions through June 26, 1998. 

First Amendment Center 
http://www.firstamendmentcenter.org 
News, commentary, and primary source materials dealing with all aspects of the first amendment. Of special interest are the the First Amendment Library and Congressional Research Service reports sections of the site. These provide links to significant court cases as well as research reports made specifically for Congress, arranged by topic area.

Religious Liberty Archive 
http://www.churchstatelaw.com 
From a law firm specializing in representing religious organizations, this site provides news, relevant cases, treatises, and applicable federal and state law regarding religious freedom in the United States. Most decisions are presented in full text, and some include legal commentary.

Landmark Supreme Court Cases 
http://www.landmarkcases.org/ 
Developed to provide teachers with a full range of resources and activities to support the teaching of landmark Supreme Court cases, helping students explore the key issues of each case. The "Resources" section features basic building blocks such as background summaries and excerpts of opinions that can be used in multiple ways.