Teachinghistory.org (National History Education Clearinghouse) offers resources to teachers in multiple ways.  Three sections outline teaching materials, history content, and best practices in teaching history.  There are links for elementary, middle, and high school teachers, with everything from complete lesson plans to general outlines of historical events and skills.  You can also access research on the state of history education in the country, as well as a blog and the teachinghistory.org community.