I chose to look at Game Classroom. The site's description on Go2Web2.0 is "Game Classroom is a one-stop web destination for accessing high-quality educational games, and homework help for K-6 students. Game Classroom offers math games, homework help, worksheets and more. It is a great site for kids, parents and teachers".
It is a great concept. I think making learning fun and interactive is important. A great thing was that there was no sign up. They had games for different game levels and subject. They even had homework help for different topics. On the down side there was no social studies games :( which is my deserved field of teaching. However there was a lot to do with language arts and math, sorry not much science either. Another downside was that some of the games are very basic. In this day in age I feel that children expect a lot out of a game format in terms of graphics.
Overall I think this would be a great tool for elementary level. The game concepts are simple but allow the students to concentrate on the content not trying to figure out the game.
Try out some of the games yourself and let me know what you think