Science Online is a site that contains lesson plans, interactive activities, worksheets and links for K-8 science. The resources are sorted by grade level and topics, such as Force and Motion, Energy, Living Things, Cells, and many more.
The site can also be used by 9-12 teachers for inspiration, other resources, and remedial work. It is also a good place to get work for students having trouble with different concepts.
Thanks to my wife, Cori, a high school biology teacher, for this resource.