Indiana University offers scanned images of many pivotal primary source documents, including the Stamp Act, a letter from John Hancock concerning the dissemination of the Declaration of Independence, and the first page from Tom Paine's The American Crisis pamphlet.
The Avalon Project at Yale Law School: 18th Century Documents
Contains several critical primary-source documents, including the Albany Plan of Union (1754); the repeal of the Stamp Act (1766); The American Crisis, by Thomas Paine (1776); and the state constitutions.
Source: The Federal and State Constitutions Colonial Charters, and Other Organic Laws of the States, Territories, and Colonies Now or Heretofore Forming the United States of America Compiled and Edited Under the Act of Congress of June 30, 1906 by Francis Newton Thorpe Washington, DC: Government Printing Office, 1909. Includes the Massachusetts Charter of 1691, several other charters, and the English Bill of Rights (1689), among others.
The American Experience offers a brief synopsis of the events leading to Revolution and a timeline of the events that led up to it and enshrined its mythology in public memory during subsequent generations.
Another American Experience site, a study of the life and correspondence between John and Abigail Adams, details their involvement with the Revolutionary War.
The Library of Congress contains several primary source treasures relating to the American Revolution and its ideological formation, including scans of the original Common Sense pamphlets
...and patriotic sermons
...and a very cool scanned image of the rough draft of the Declaration of Independence, which includes editing marks by John Adams and Benjamin Franklin!
...the papers of George Washington, an on-line version
...the Thomas Jefferson papers
The papers of John and Abigail Adams and the Adams family
The Benjamin Franklin papers