About Government
http://aboutgovernment.org
"Explore the diversity of Web-based information about the Federal Government through the AboutGoverment portal site..."
As a portal site, About Government offers a good breakdown of historical sites by categories. With over 250 sites listed categories include: general history, Articles of Confederation, Bill of Rights, Federal Papers, Declaration of Independence, and the United States Constitution. With any portal site however, one must be careful about where exactly they are being directed to. About Government is a good website with a lot of constitutional history links, but as it states on the website, they will not be accountable for the information posted on the other sites.

Core Documents of U.S. Democracy
http://www.access.gpo.gov/su_docs/locators/coredocs/
"To provide American citizens direct online access to the basic Federal Government documents that define our democratic society"
This website is a service brought to us by the Superintendent of Documents at the U.S. Government Printing Office. This is an easily navigated site that offers categories such as Cornerstone, Congressional, and Presidential Documents. While this site is primarily a portal site that directs you to other sites for the information, those site that it does direct you to seem to be creditable, well-established sites. As an educator, one good thing about this site is that you can suggest a document to them for inclusion onto their site, so in theory it would seem that this site could continue to grow and expand in what it is able to offer.