Here are some fun websites.

General

• ALEKS 
• CrashCourse
• Kahn Academy
• PBS Kids
• SparkNotes

Mathematics

• My kids’ favorite: Cool Math Games 
• Cyberchase on PBS Kids 
• FunBrain 
• Math Magician Games
• Math Playground 
• Multiplication Games
• NUMBERNUT
• Paul’s Online Math Notes
• PurpleMath

Mathematics & Science

• The Biology Project
• ChemWiki
• PhET: Interactive Simulations in Science and Math
• Physics Classroom
• Physics Games
• Review: Physics Games
• My son’s favorite: Surgeon Simulator

Resources

• Help Your Child to Succeed in Math, NCTM
• Programs for Students, AMS
• Why Do Math, SIAM