The Librarian's Mantra
Besides this blog, there are other websites that will lead you to a WEALTH of primary sources, old and rare books currently out of print, and digitized manuscripts.
On my blog The Foundation Forum, I have a very long list of links on the left sidebar which are extremely useful for researching original resources. Below, I will list and describe those which contain the most helpful amount of information.
Selected Documents from the American Colonial Era
This is apparently a page from a college history course online for college student studying early colonial history. I link to it, however, because it provides valuable documents from the pre-Revolutionary era, including a pamphlet by William Livingston in defense of the Great Awakening evangelists.
Archiving Early America
Of course, contains many documents from the Founding Era. Also features online videos of classic moments in American Revolutionary history, based upon bona fide documentation.
Avalon Project at Yale Law School
This is one of the most frequently-used sources for original sources on the Internet. In addition to containing the texts of the books which influenced the writing of our Founding Documents, the Founding Documents themselves, the various state constitutions, the Avalon Project also features the notes of the delegates who attended the Constitutional Convention, as well as the speeches and addresses of those of our Founders who became President of the United States.
A Century of Lawmaking (1774-1875)
This is one of the most valuable sources of primary documents made available by the online Library of Congress, American Memory. With this collection, the average individual can search or peruse the debates and proceeding of Congress from its very beginning. Also featured are several works which republished the debates which framed the Constitution, as well as the private and business letters of the delegates to Congress and the Constitutional Convention.
Cornell University Library "Making of America"
This collection hosts a huge collection of works from, about, and after the Founding Era. Though the writings displayed are from the digitized images of books, magazines, newsletters, and pamphlets (and therefore cannot be highlighted with the cursor), Cornell has made it possible for the reader to search the entire collection.
University of Michigan Digital General Collection
The format of this collection is very similar to the Cornell Project above, however, it covers a much broader scope of works. This is a truly valuable resource for finding extremely readable digitized books which have gone long out of print. I use this resource frequently to read or search old biographies or editions of the writings of the Founders, of Presidents, or the diaries and autobiographies of people who lived during those times. This collection spans beyond the Founding Era and into the present.
Gilder-Lehrman Institute of American History
Hosts a collection of digitized letters and prints throughout the span of American history. Transcripts are available for most documents, and the Institute may be contacted via email for more information, or for transcripts of certain documents.
A User's Guide to the Declaration of Independence
Hosts a selection of writings from influential Founding Fathers, as well as the sermons and pamphlets of others who influenced American public thought. Includes key letters by the Founding Fathers on key political issues of their day.
Internet Text Archive
Much of my frustration in being unable to access rare and out-of-print books was relieved when I discovered this website, and how to use it. It features the digital images of books which have hardly seen the light of day for a century. Some of the images are in better condition than others. Each book may be searched individually; HOWEVER, trying to find a key phrase may prove troublesome, because the search engine will locate every place where each of your individual words is found in the book. If you are looking for a quote or passage, I would recommend that you use just one unique word (omit any and all a's, an's the's, etc), and not any phrases.
Laws of Nature and Nature's God
The scholars who host this site seem to be a bit opposed to the "Christian nation" thesis; however, several of the books which influenced our Founders political thought are available here, and so I use their site for research.
Liberty Library of Constitutional Classics
Contains documentary history of American law, which documents are available in a variety of formats. Also includes important writings and key letters of the Founding Fathers.
University of Michigan "Making of America"
A division of the Digital General Collection (see above) which deals specifically with American history.
Online Library of Liberty
This is an increasingly popular source of primary sources, and is hosted by Liberty Fund. In addition to featuring the texts of collections of the Founders' writings, it features the works of other political, philosophical, and economical writers before and after the Founding Era. Also includes the writings of the leaders of the Reformation, as well as the various books of the Bible. Liberty Fund recently added a very convenient search feature to each individual set of writings, as well as to the website.
Primary Source Documents Pertaining to North American History
Fantastic documentary guide to America's Christian and political history.
A website that "publishes" online books of the past and the present; therefore, includes books about and by the Founding Fathers.
Their Own Words
A base of digitized search-able old books and pamphlets, hosted by Dickinson College (founded by Founding Father Benjamin Rush).
Digitized documentary history of American society and law.
English Literature: Restoration and 18th Century
A collection of the works of the leading figures of England before and during the Founding Era.
Digitized digital history from Revolution to present.
A source of selected rulings of and cases before the United States Supreme Court, both from the past and the present.
19th Century Schoolbooks
Learn what education was like after the Founding Era by reading the textbooks in American public schools from the 19th century.
United States History Documents
A documentary history of the United States.
The National Archives
Hosted by the United States National Archives in Washington, D. C.
Supreme Court of the United States
Website of the United States Supreme Court containing information on the Court, its members, and the cases before it presently.
Teaching American History Library
Documents from American history hosted by "Teaching American History."
This Nation Library
Landmark documents, speeches, and Supreme Court cases throughout American history hosted by ThisNation.com.
The U.S. Constitution Online
Information about the Constitution of the United States of America.
I hope this list of resources proves helpful to anyone searching for documents and doing other research. If you need more information, please feel free to ask questions via the comments section, and I will get back to you as soon as I can.