As Many Exceptions As Rules is a cool blog that posts weekly about little known science facts and updates. Check it often.
Biology4Kids--play and learn about cells, microbes, plants and animals
Chem4Kids--play and learn about matter, atoms, elements, reactions, biochemistry. Also in Spanish.
Cosmos4Kids--play and learn about universe, galaxies, stars, systems, solar system, and space exploration
Geography4Kids--play and learn about earth structure, atmosphere, hydrosphere, biosphere, BGC cycles, climates
Physics4Kids--play and learn about motion, heat, electricity, light, and other modern physics
The Virtual Body for biology classes
The Chronology of Events in Science, Mathematics, and Technology
How Stuff Works covers natural phenomena and mechanical functions
Live Science has news about science.
Make your own temperature scale
Take Care of Texas has environmental tips for Texans.
Simulations
Free Science Videos