Strongest in the physical sciences, LibreTexts gathers OER materials from across the web, and congregates them into one site broken down by discipline. They offer open resources and a platform for remixing, curation and publishing of your own.
A collection of high quality, free-to-use courses that you can download and use for teaching. All content is stored in Google docs. A project of the Washington State Board for Community and Technical Colleges and the Gates Foundation.
Open Library is an open, editable library catalog, building towards a web page for every book ever published. Digitized fiction and nonfiction e-books are available for checkout, sometimes with a waitlist.
OER leader Dr. Larry Green's list of OER used by faculty at different colleges, pulled from years of the Community College Consortium for Open Educational Resources listserve and organized by discipline.