New York Science Teacher is a great site created by a science teacher, for other science teachers. It has science labs, demonstrations, lesson plans, resource links, worksheets, activities and much more.
It is organized by subject area: astronomy, biology, chemistry, elementary, earth science, geology, environmental, meteorology, physical science, and physics.
It is also organized by category: reference tables, Regent's prep, labs, worksheets, review games, misconceptions, and much more.
It is a great resource for any science teacher.
(Thanks to my wife Cori, a high school Biology teacher, for finding this site)