The American YAWP- A massively open, collaborative American history textbook by experienced college-level instructors who volunteer to help democratize the American past for modern classrooms.
The Big History Project- Big History is a social studies course that spans 13.8 billion years. It weaves insights from many disciplines to form a single story that helps us better understand people, civilizations, and how we are connected to everything around us.
Michigan Open Book Project- Click on "The Books" and then on grade level.
Beyond the Bubble- uses the Library of Congress archives to create History Assessments of Thinking.
C3 Teachers- Lessons with embedded primary sources, based on the Inquiry Arc of the College, Career, and Civic Life (C3) Framework for State Social Studies Standards, and licensed under Creative Commons.
Stanford History Assessments- free to download and use once you make an account
Georgia Virtual Learning History Lessons- Unless otherwise stated, content is licensed by cc-by-nc-sa.
Digital Public Library of America
Al Jazeera Creative Commons Repository: broadcast quality footage released under creative commons licensing
Time Maps: free to use and share, non-commercially, as long as the maps are hyperlinked with the exact page from which the map was taken, all text is referenced with "TimeMap of World History," followed by the exact web address from which the info was taken, the logo is not removed or obscured, and links to the map appear near the map or in a references section.