The Open Educational Resources Initiative of the Academic Senate of California Community Colleges has an excellent list of OER resources arranged by discipline. These materials have been curated by ASCCC OERI discipline experts.
The Mason University OER Metafinder searches 22 different OER repositories, including BCcampus, MIT OpenCourseWare, OER Commons, OpenStax, HathiTrust and Open Textbook Library. The search tool works the same as OneSearch: type in a subject or title to find available OER options.
Below is a list of additional resources available that provide open materials:
LibreTexts: LibreTexts provides access to OER resources and a platform for faculty to curate and compile resources. LibreTexts is based at UC Davis.
Open Course Library (OCL): OCL materials were created through Washington State Board for Community & Technical Colleges grant, but are freely shared to the world with a Creative Commons Attribution-only license (CC-BY).
Creative Commons: Creative Commons is a global nonprofit organization that enables sharing and reuse of educational materials, provided that proper credit is given to the originators.
MERLOT: The MERLOT collection consists of tens of thousands of discipline-specific learning materials, learning exercises, and Content Builder webpages, together with associated comments, and bookmark collections, all intended to enhance the teaching experience of using a learning material.
COOL4Ed (California Open Online Library for Education): "A collection of Course Materials Showcases where faculty, staff, and students can find free and open educational resources aligned with 52 CID courses." In addition to many more resources.
OER Commons: "From a single point of access in OER Commons, you can search, browse, and evaluate resources in OER Commons' growing collection of over 50,000 high-quality OER."