Here are some general science sites for you to enjoy.
Science Explorations from Scholastic
Bitesize Science from the BBC
Funology: the science of having fun
Exploratorium: the museum of science, art, and human perception
MHSchool: a variety of activities from science books
Ology from the American Museum of Natural History
FOSSWeb for grades K-2
FOSSWeb for grades 3-6
Biology 4 Kids: learn about cells, plants, and animals
Hunkin's Experiments: cartoons provide lots of experiments to try at home
American Museum of Natural History - learn about different "ologies"
TVS Techno Wizards
Trinity Valley School