If you like word analogies, check out this site. http://www.factmonster.com/
Learning about bridges. http://www.pbs.org/buildingbig
Learn about bats. http://www.bats4kids.org
Archaeology: Puzzled by the Past http://www.history.org/kids/games/dirtDetective.cfm
Archaeology: Puzzled by the Past http://www.nps.gov/webrangers/activityList.html