Here are couple of cool Google Maps Mashups which tests your World Geography Knowledge

World Geography Quiz: This quote from the website:

You’ll be asked for the locations of various randomly selected national capitals and cities with a population over 100K. Pan and zoom (with the left mouse button and the on-map controls) then drag the marker to where you think it is. How far off you are will then be displayed.

TerraClues: Quoting TerraClues Website

TerraClues is a puzzle game where the objective is to find locations on the world map by solving a set of clues. Each time you solve a clue, the next clue will be unlocked until all clues have been solved. (via GoogleMapsMania)