How a bout a bit of Geography lesson all wrapped up in a game? Here are two apps.
The first one focuses on continents and oceans. First it teaches the words on an interactive map. In a second phase the students gets to test their knowledge. Check out ilearn’s Continents then go to developer site and see all the other ones, including Europe and Middle East.
The second app, Stack the Continents / Lite is a bit more challenging. You need to know a few things about the US states. Then you need to be able to stack those states that you got right. Not something I am very good at. My stacking hight is not something to show off with, but the know how about the states is definitely growing!
Also watch out for Stack the countries / Lite