• National Geographic: Lewis & Clark Megasite
• Lewis & Clark @ nationalgeographic.com
• PBS Online - Lewis and Clark
• Lewis and Clark National Historic Trail
• Lewis and Clark Trail Heritage Foundation
• The National Council of the Lewis & Clark Bicentennial
• National Signature Events
• The Discovery Expedition of St. Charles, Missouri --
  Official Reenactors for the National Lewis & Clark Bicentennial
• Lewis and Clark Bicentenial Commemoration, Falls of the Ohio
• Meriwether Lewis Rides Again
• Discovering Lewis and Clark
• Lewis and Clark Maps from the David Rumsey Historical Map Collection

Probably the best single book for older Scouts and adults to read about the Lewis and Clark Expedition is Undaunted Courage: Meriwether Lewis, Thomas Jefferson, and the Opening of the American West by Stephen E. Ambrose, published by Simon & Schuster, 1996.

For a very good list of other publications, including Children's Books, check out the National Park Service suggestions at Relevant Books and Publications.