This site from the National Endowment for the Humanities is a rich resource for materials and lesson plans in History and Social Studies, The Arts, Civics and Government , and Literature and Language Arts.
Great site (thanks Robin!) for asking your students to explore graphs populated with real world data. Amazing number of categories to explore and compare with each other to find correlations. Even more amazing is the "PLAY" button that shows your chosen relationships as they have changed over time.
This extensive document collection can be used as the take-off point for lessons in almost any discipline. The site provides great teacher resources for teaching with primary source documents, including lesson plans.
Tremendous resource for Washington State History. The site has creative lesson plans to offer teachers, curriculum enrichment materials and field trip information for the museum located in downtown Seattle.