The Avalon Project: The American Constitution--A Documentary Record – Yale Law School – Documents on the roots of the Constitution, the Constitutional Convention, and the formation of the government.
Documents from the Continental Congress and Constitutional Convention – Library of Congress – Documents relating to the work of the Congress and the drafting and ratification of the Constitution; includes extracts from the journals of Congress, resolutions, proclamations, committee reports, treaties, and early printed versions of the United States Constitution and the Declaration of Independence.
Louisiana: European Exploration and the Louisana Purchase – Library of Congress – A collection of primary sources, including many maps, that focus on the region covered in the Louisiana Purchase.
The Thomas Jefferson Digital Archive – University of Virginia – Letters written by or to Thomas Jefferson, as well as compilation of quotations from Jefferson's writings.