tokisto: Railroad Tycoon series give a good amount of true facts about, well, railroads, trains, tycoons, USA formation, relations between UK and India and others.
Tropico is a goofy way to discuss Cold War and political regimes in Latin America.
There are the American Conquest and Cossacks games about conflicts invaders (settlers) and natives in the first and the independent slavic groups in the second.
Papers, Please could be one too (all the ones that I mentioned are heavy political-biased games).
They are not educational per si, but can be used to invoke interest in the theme
Waking Mars is an outstanding game about spacial exploration, botanics, alien life and so on, worthy a look
PS.: And for you I recommend No Pineapple Left Behind :p