Here is a list of science websites that could be beneficial to be used at home of during brain break/free time in the classroom.
Anatomy Arcade
Animal Planet
Bill Nye
Climate Kids
CK-12
Dr. Universe
Exploratorium
Fun Learning for Kids
Funology
Hero Elementary
Howtosmile
Jet Propulsion Laboratory
Lawrence Hall of Science
Memphis Zoo
National Geographic Kids
National Science Digital Library
Ok Go Sandbox
OLogy
PBS Kids
PhEt Interactive Simulations
Planet Pals
Project Noah
Raising Dragons
Science Bob
Science Buddies
Science Friday
Slooh
Space Place
Turtle Diary
Weather Wiz Kids