ProQuest History Study Center
National Geographic for Kids
Good starting point for online geography work.Fun site with geography games, activities, etc.
Library of Congress
You can explore for a month through the American Memory Collection and the Online Exhibits, and still not see all the cool stuff located here.
Outline Maps
Outline Maps

PCL Map Collection
A collection of outline and base maps for continents, world regions, countries and states.
Smithsonian For Kids
History for Kids
World Facts
Country Studies
Lewis and Clark iSpace
Journals of Lewis & Clark Expedition
Discovering Lewis & Clark
National Geographic - Lewis & Clark
OPB - Lewis & Clark
Lewis & Clark as Naturalists
Lewis & Clark - Mapping the West
Lewis & Clark - Trail Heritage Foundation
History with a Tribal Perspective - Lewis & Clark Trail
Discovery and Exploration - Maps