The United States Constitution and Other Historic Documents:

• The Code of Hammurabi
• Blackstone's Commentaries by Tucker  (written in 1803, with notes relating the commentaries to the laws of the United States)
• Declaration of Independence, Indiana University Law School site
• Articles of Confederation, Yale Law School site  (includes discussion by Thomas Jefferson from his autobiography and link to the Madison Debates)
• Declarations and Resolves of the First Continental Congress, October, 1774
• Documents From The Continental Congress And The Constitutional Convention - Library of Congress
• Debates in the Convention of 1787, by James Madison  (proceedings of the Constitutional Convention of 1787 leading to the adoption of the US Constitution, beginning with the first day....searchable here )
• The Federalist Papers Online, FoundingFathers.info
• FindLaw Constitutional Law Center  (The US Constitution annotated, plus links to materials on the Founding Fathers, the Articles of Confederation, and the Federalist Papers)
• GPO Site...The Constitution Annotated...by the Congressional Research Service
• Web Guide to the Constitution of the United States
• Constitution of the United States of America, National Archives Site
• FindLaw Constitution Search (search engine for the U.S. Constitution)
• National Archives and Records Administration's "Our Documents" - Milestone Documents  (Constitution, Declaration of Independence, Federalist Papers, plus many others, such as the Lee Resolution, the Virginia Plan of 1787, the Northwest Ordinance of 1787, Articles of Confederation, Treaty of Paris, etc)
• U.S. Congressional Documents and Debates, 1774-1873  (searchable archive of scanned images and full text of nine separate government documents covering the period from the Continental Congress, the Constitutional Convention, and the First through Twelfth Federal Congresses. It includes the House Journal, Senate Journal, Annals of Congress, Journals of the Continental Congress, Elliot's Debates, Farrand's Records, Maclay's Journal.)
• Hinds' Precedents of the House Of Representatives of the United States