Ambrose, Stephen E. Undaunted Courage: Meriwether Lewis, Thomas Jefferson, and the Opening of the American West. New York: Simon and Shuster, 1995.
A comprehensive, thoroughly researched review of the Lewis and Clark Expedition
Andrist, Ralph K. To the Pacific with Lewis and Clark. New York: Harper and Row, 1967.
Blumberg, Rhoda. The Incredible Journey of Lewis and Clark. New York: Beech Tree, 1995.
DeVoto, Bernard. The Journals of Lewis and Clark. New York: Houghton Mifflin, 1953; 1997.
Important introduction to this edited version of the journals.
Moulton, Gary E., ed. Atlas of the Lewis and Clark Expedition. Lincoln, Neb.: University of Nebraska Press, 1983.
Excellent compilation of maps with an excellent introduction.
Site of the Academy of Natural Sciences where many of the specimens collected by Lewis and Clark are still held. Links to the Lewis and Clark exhibits and archives.
Philadelphia Connection, Contributions of Philadelphia to Lewis and Clark History Part II– Postlude (1807- 1814) http://www.lewisandclarkphila.org/philadelphia/philadelphiapostlude1.h...
The link, part of the Lewis and Clark Heritage Trail Foundation website, describes the Philadelphia connection in telling the Lewis and Clark story.
The Journals of Lewis and Clark, In the Footsteps of Lewis and Clark. http://www.sierraclub.org/lewisandclark/journal/
Chronologically catalogued journals entries of Meriwether Lewis and William Clark.
The Journals of Lewis and Clark: Table of Contents, Lewis and Clark: Table of Contents http://xroads.virginia.edu/~HYPER/JOURNALS/toc.html
Catalogued journals of Lewis and Clark with printable version available.
The Lewis and Clark Journey of Discovery, The Journey http://www.nps.gov/jeff/LewisClark2/TheJourney/TheJourneyMain.htm
Provides a comprehensive overview of the expedition and specifically address the goals of the journey in the areas of mapmaking, science, native peoples, paleontology and archaeology
Treasures of the APS, Cross country in 1804-1806 http://www.amphilsoc.org/library/exhibits/treasures/landc.htm
American Philosophical Society site that gives an overview of the documents and specimens they hold from the expedition.