BrainPop.com
Fact Monster
Fun with phonics and words
Toon University
Brain Teasers
Dr. Universe (Science questions and answers for kids of all ages!)
"Get help preparing for for SAT, ACT and GRE exams. Number2.com's online test preparation courses are free. By creating an account you can access a customized course that includes user-friendly tutorials, practice sessions that dynamically adapt to each student's ability level, a vocabulary builder, and more..." http://number2.com/