I am now teaching Science! It has been about 7 years since I have taught since so when I come to any good sites I will add them here:

WonderQuest - website that is has questions and answers about many different topics

BBC Schools- Primary grades - activities for ages 4-11
BBC Schools- health, forces, plants and animals, using electricity and more
BBC Schools- teeth and eating, rocks and soil, magnets and springs, and more
BBC Schools- moving and growing, keeping warm, solids and liquids, and more
BBC Schools - keeping healthy, life cycles, gases around us, changing sounds, changing states, and more
BBC Schools- adaptation, micro organisms, forces in action, how we see things, changing circuits

The Yukiest Site - great site for Science - games and info
Discovery Kids - games, videos, and more
Science Games - lots of Science games
Classify - mammals, plants, birds, and more

Earth and Sun:
Revolution of the Earth - great website!
Earth Games- games about the Earth's features