A highly addictive game which I stumbled upon facebook (as an app) was the TRAVELER IQ Challenge. I feel that this game (The original link is: http://www.travelpod.com/traveler-iq) can be a great tool for learning about different locations (give or take 200-300 miles).
The reason is because I feel that the map projection system used by this site uses one of the standard but slightly misleading map projection systems which show all parts of the world with similar areas. This does not show the large distances on Equator or the closeness of spots in the polar region exactly to scale. For example, Greenland is shown as big as Africa, but in fact Africa is 14 times the size of Greenland.
(Trivia: I have a friend who has lived in Greenland doing research and I have had coffee with at Webster's cafe)
By the way, you can read more about Mercator map projection here.
But still, you can play the game and discover interesting places like Palau or Mt Krakatoa and all this without registering. If you want to keep track of your score, then you can add it on facebook.
Of course the world map game is highly random (ie from all places on earth), but at the top region of this website you see several country specific challenges (e.g N America, Africa, or even world photos) that can be very useful to geography teachers.
This can also be a great after dinner game played at geeky parties, esp. the world photos game!
Good luck and Happy Traveling.