A blog and website designed by Bruce Kauffman where he discusses different facts and stories from history. This website includes all kinds of testimonials and historical knowledge that would be great for a high school teacher.
A layout of activities, sources, and vocabulary that deals with the concept of World War II. It also includes the goals that each activity accomplishes so teachers can gauge what they have and have not covered.
A whole lesson plan with discussion topics and questions for your students and an activity for them to help them understand the concept of national security.
While it may seem common sense, looking at Wikipedia's "Today in History" section on the front page everyday is a way to engage students into history and make them reflect on the events that happened that day years ago.
A compliation of historical documents from the University of Oklahoma's College of Law. Free and accessible makes this a good page to have on hand when in need of some primary sources for the classroom.
Discovery has created an entire list of topics with free lesson plans for history teachers. Each topic breaks down the lesson and teachers could use this as little or as much as they need.