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.
the 35 best speeches in History including an excerpt from each one. It's from a joke website but nevertheless it still lists some speeches that can be used in the classroom.
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.
This is a historical website that leads you to other websites that are specific to your section of history that you are teaching. It provides facts and lesson plans for helping your students learn.
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.