These five resources will get you the most results and are used by many librarians and instructors. However, currently there is not a preferred OER directory and sometimes things slip through the cracks, so the library would be happy to help you search.
Open Textbook Library: Over 1000 textbooks on a variety of subjects. Open textbooks are licensed by authors and publishers to be freely used and adapted. Download, edit and distribute them at no cost. The Open Textbook Library is supported by the Open Education Network. It includes books from OpenStax.
The kitchen sink of OER, these repositories house both textbooks and other learning materials, such as courses, learning objects like media, assignments, syllabi, and more.
After looking over guides from other libraries, the following three contain every resource you could want. There will be some overlap. I will only add additional links if they aren't on one of these three or deserve extra attention.
Open RN - Open Resources for Nursing | Chippewa Valley Technical College: One of the big resources for Nursing OER developed with a huge grant. More are being added.
Open at Scale Nursing OER Spreadsheet: Lists many resources individually. Download to sort.
Projected 2024: Open Educational Resources Nursing Essentials (O.N.E.) Project - | OERTX
The Directory of Open Access Journals is a website that hosts a community-curated list of open access journals, maintained by Infrastructure Services for Open Access. It contains over 15,000 journals covering all areas of science, technology, medicine, social sciences, arts, and humanities. Open access journals from all countries and in all languages are welcome in DOAJ.
PLOS is a nonprofit open-access science, technology, and medicine publisher with a library of open-access journals and other scientific literature under an open-content license.
PMC is a free full-text archive of biomedical and life sciences journal literature at the U.S. National Institutes of Health's National Library of Medicine (NIH/NLM)