Sheppard Software offers online geography games at a variety of age levels and knowledge levels. There are sections for US and World geography. What I especially like is that they have games that actually TEACH not just test knowledge of geography.
World Wonders Project
World Wonders Project - "The Google World Wonders Project is a platform which brings world heritage sites of the modern and ancient world online. Using Street View, 3D modeling and other Google technologies, we have made these amazing sites accessible to everyone across the globe. With videos, photos and in-depth information, you can now explore the world wonders from your armchair just as if you were there." There are also teacher guides to assist with using this tool in education.
Free Technology for Teachers has a long list of free fun geography games online. In addition to playing the games you can make some of your own using these resources.