The Directory of OpenAccess Books (doabooks.org/doab) – Search this website to find free, downloadable books covering a wide array of topics.
FlatWorld Knowledge (catalog.flatworldknowledge.com) – Personalize textbooks by rearranging, adding, and deleting content to match your syllabus.
HathiTrust (hathitrust.org) – According to their about page, HathiTrust is "partnership of major research institutions and libraries working to ensure that the cultural record is preserved and accessible long into the future." The full text of many older books are freely available, some content is limited to HathiTrust partners.
Lumen Learning (courses.lumenlearning.com/catalog/lumen) – Lumen provides a variety of learning content to be used as-is or modified for your particular needs.
Merlot (merlot.org) provides links to online, peer-reviewed teaching and learning materials. You can personalize and share collections of linked content.
The National Academies Press (nap.edu) – Provides freely available content to which instructors can link.
Open Access Publishing in European Networks (oapen.org/home) – The OAPEN Library contains freely accessible scholarly monographs.
Open Textbook Library (open.umn.edu/opentextbooks) – Includes links to peer-reviewed books.
OpenStax (openstax.org) - Openly-licensed textbooks.
Nominate other excellent OER that you use as an instructor or learner! Emailrescott3 AT memphis.edu