Charles A. Dana Center
Math and science search engine, particularly focusing on clarification of lessons and providing lessons for teachers, called TEKS toolkit. It also provides worksheets and games for classroom enhancement. The parent site is a research project for learning improvement, so papers and news concerning learning improvement can also be found on this site. (The TEKS toolkit can also be purchased for more information than just online pdf's. Just go to the parent site http://www.utdanacenter.org/
and click "products" on the toolbar.