Where in the USA is Carmen Sandiego - classic game using US geography to solve cases
Where in the World is Carmen Sandiego - just like the one above but with world geography!
Oregon Trail - combines math with history and economics to get settlers across the United States in the 1800s
Ameriquake - matching US states
Various US Geography Games
USA Learn Together - matching games for states, capitals, abbreviations
Mr. Nussbaum's US Geography page - various elementary games for learning US geography