The United States Geological Survey offers posters, teaching packets, references, and all sorts of other goodies at this site. A definite must-see for all earth science teachers. It has great graphics and discusses the science behind the demonstration. This site from the USGS is dedicated to the topic of water for K-12 students. It includes an interactive center with quizzes and exploratory sessions, plus pictures, data, maps and other educational materials to be used in the classroom.
Students can complete the activities on the site and receive a certificate of completion.
This site has links for math lesson plans and activities ranging from grades K-10. Lots of interesting stuff here.