(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
(pre-K to 6): This site has versions in 5 languages, and 9 categories of activities, including Games, Learn to Draw, Listen and Reading Comprehension, Learn to Draw the Numbers, and so on. It appears to be predominantly spanish based on the ads that surround the playing area.