Gooru is a site I wrote about this past February that was in private Alpha. I just received notice from them that they have now launched their Beta site and it's open for use.
Gooru is a search engine for education and learning. It contains study guides, aligned to standards and personalized, on topics in 5th - 12th grade math and science. Resources include videos, animations, links, digital textbooks, and more. All of the resources have been organized and reviewed by teachers or content experts.
Here's a small sample of what a search for "physics" returns:
It also contains a social aspect with a community to discuss topics and ask questions. There are also self-assessments that Gooru suggest resources and study guides to help you.
Check it out and share with your students: http://www.goorulearning.org/gooru/index.g#/home