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
https://www.govinfo.gov/
From the Congressional Research Service, Library of Congress.  An annotated text, incorporating Supreme Court decisions through June 26, 1998. 

First Amendment Center
https://www.freedomforum.org/the-first-amendment/
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. 

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.