Images for Christopher Columbus.
http://www.imahero.com/../photos/chriscolumbus_main.html

http://www.mariner.org/educationalad/ageofex/columbus.php

http://www.loc.gov/exhibits/1492/

Images for Sacagawea.
http://www.imahero.com/../photos/sacagawea_main.html

http://www.imahero.com/../../timelines/sacagawea_timeline.htm

http://magma.nationalgeographic.com/ngm/0302/feature4/index.html

Images for Lewis & Clark.
http://www.lewisclark.net/

http://www.lib.virginia.edu/small/exhibits/lewis_clark/introduction.html

http://www.pbs.org/lewisandclark/archive/time/