Math
Math Brain: Random math games for kids
Math Magician: Practice math facts by operation
Multiplication.com: Games to practice basic facts
SumDog: Play math games against classmates and others worldwide!
StudyJams Math: Watch math tutorial cartoons
Jefferson Labs:  Take practice SOL tests


Language
Story Bird: A site where kids can write and publish books
Spelling City: Practice spelling and vocabulary


Science
Weather Wiz: A great site for weather obsessed kids
PHET: Play with science modules online
StudyJams Science: Watch slideshows and cartoons on science topics


Social Studies
SOL Pass: A great site to review concepts


Application
Type to Learn: A site that teaches finger positions for typing