(Grades 3 and up): This site features a variety of games and interactives and leans towards various science and history based adventures and activities, rather than the traditional subjects-specific types of games on many other sites. There's a lot of cool stuff here, like Fossil Hunts, Journey to the Edge, Rhino Rescue, Monster Fish of the Congo, Earth in Balance, and How Taboo are You?
(Grades 3 and up) : Karooba is a "social and gaming site that is focused on education", featuring canned and custom developed Quizzes, Trivia and more. You really have to register to get the most out of it