Before searching begins, the obvious first step is to identify the learning goals of your course, and what types of resources you will need. Once that knowledge is in hand, several portals exist to help instructors and course designers find appropriate open educational resources. Some focus specifically on textbooks, while others are repositories of all sorts of open resources.
George Mason University has built a metasearch tool that searches more than twenty of the most popular sites for open resources. Initial search results can be narrowed by facets, including sub-disciplines, publication dates, and many more.
The California State University System, in partnership with other educational institutions and professional societies, moderates a collection of OER resources called MERLOT II. In this community, members freely share OERs, as well as resources and tools to help with OER creation and sharing.
"OER Commons is a public digital library of open educational resources. Explore, create, and collaborate with educators around the world to improve curriculum."
The National Science Digital Library provides a collection of sharable undergraduate educational resources for science and mathematics. Called iLumina, it contains a variety of resources, from individual images and videos to complete courses.
These collections of complete textbooks include contributions by authors from many institutions, not just the host schools.
The Open Textbook Library is sponsored by the Center for Open Education at the University of Minnesota.
OpenStax is a textbook collection hosted at Rice University.
Saylor Academy offers a variety of free and open textbooks.
Countless free learning resources are available online, in almost every subject. Here are some sites that help with finding quality materials to supplement texts or use as building blocks to meet specific learning objectives.
Many other collections and sites exist beyond these examples. Ask your friendly library staff for help locating more resources in your discipline.