K12 Station features a collection of links from several content areas including science, math, English, arts, and more. The science links are organized by grade bands: K-2, 3-5, 6-8, and 9-12. Once you click on a grade band you find links organized by big ideas in science.
Applications for Science Teachers: Yet another collection of great links for K-12 teachers. These could be used for lesson plan ideas, supplementary instruction, extensions, homework, research, etc. Lots of good stuff here- I recommend adding this to your bookmarks. Elementary teachers will find sites to support other content areas as well.