"Open Educational Resources (OERs) are any type of educational materials that are in the public domain or introduced with an open license. The nature of these open materials means that anyone can legally and freely copy, use, adapt and re-share them. OERs range from textbooks to curricula, syllabi, lecture notes, assignments, tests, projects, audio, video and animation." - UNESCO
As the definition above illustrates, OER are not limited to only open textbooks; however, textbook affordability is a central issue for many OER initiatives.
If you'd like to learn more about OER and textbook affordability, visit the Open Educational Resources and Affordable Textbooks guide.
The Milne Library at SUNY Geneseo developed OASIS, a tool that searches across multiple OER sites.
The TED Talks listed below are available under a Creative Commons license. For complete information about how TED Talks can be used, visit the TED Talks Usage Policy page.
The Library of Congress holds many collections that contain film and video. Though not all items within the collections are openly licensed or in the public domain (i.e. free of copyright), they are available online for educational and research purposes.
Below are links to a few of these collections, but there are many more on the Library of Congress' website at the above link.