Edmodo is a social learning network similar to Facebook but designed for educators to use for course management. Virtually all communication concerning homework and assessments for my courses this year will be delivered through Edmodo.
This useful website contains many explanations for "how stuff works." All of the articles are written by experts and relevant professionals.
The Khan Academy is a non-profit organization that develops online, educational, video lessons which they post, by subject and topic, on their website. Their list of physics lessons is extensive.
Zona Land Education is a physics and math website. They give thorough, step-by-step instruction for a variety of topics.
"The Star City Astronomy Network (SCAN) is a group of astronomy enthusiasts that actually spend time observing the night sky. There are no 'armchair astronomers' here."