Or distance learning is a field of education that focuses on the pedagogy/andragogy, technology, and instructional systems design that is effectively incorporated in delivering education to students who are not physically “on site” to receive their education. Huge resource on Wikipedia.
Free Online Course Materials | MIT OpenCourseWare
A web-based publication of virtually all MIT course content. OCW is open and available to the world and is a permanent MIT activity.
Free University Project
Guided independent study materials produced by the site or through links on the internet that can lead to college credit by examination.
Open Textbooks « Community College Consortium for Open Educational Resources
Most of the textbooks on this list have Creative Commons (CC) open licenses or GNU-Free Document License. Others are U.S. government documents in the public domain (PD).