PUBMED
Understanding Science from the University of California
PhET from the University of Colorado delivers thousands of simulations for physics, chemisty, and biology
Discovery Education
How Stuff Works
Sparticl is a collection of the very best the web has to offer in science, technology, engineering, and math or STEM. Sparticl includes answers to science questions, images, videos, games, and hands-on activities, all curated by a team of experts.