The journals of Lewis and Clark—among of the most exciting primary sources in American history—are now available in searchable format online. Not to be missed by anyone interested in learning more about the voyage of discovery.
National Geographic magazine has created a fascinating interactive online exhibit on Lewis and Clark. Especially strong on Lewis and Clark's scientific discoveries and observations, the site features extensive excerpts from the Captains' diaries and a fascinating inventory of all items carried by the Corps of Discovery. For the record, they carried eight brass kettles, 4,600 sewing needles, 176 pounds of gunpowder, fifty dozen of Dr. Rush's patented "Rush's Thunderclapper" pills, and one copy of A Practical Introduction to Spherics and Nautical Astronomy.
As a companion to Ken Burns's documentary, Lewis and Clark, PBS has constructed a fine website that meets their usual high standards. A fun interactive trail map is but one of dozens of interesting features.
The folks who run the museum at Thomas Jefferson's estate at Montiecello, Virginia, have created an online exhibit that contextualizes the Lewis and Clark expedition within Jefferson's broader vision of a larger "Empire of Liberty" in the American West. Be sure to check out the full text of Jefferson's instructions to Meriwether Lewis.