Free Rice: Each time you answer a vocabulary question correctly, 10 grains of rice are donated to the World Food Programme!
BrainHQ: Developed by neuroscientists and brain experts, the games in BrainHQ have been designed to help with train your brain! (Sign-up required)
Nobel Prize Games: Games based upon on the research of Nobel Prize winners. (They're fun!)
Codecademy: Learn to code on an interactive platform! (Sign-up required)
K-12 Games and Quizzes: Gov. site that includes such fun games as : Name that State, Spot the Difference and Memory.