There are MANY places online where you can find OER. Below are some good repositories and search tools to get started. If you need additional help finding OER for your course, contact your liaison librarian.
The following resources primarily contain high quality open textbooks (mostly peer-reviewed) across various subject areas.
The following resources contain other types of OER, such as syllabi, course handouts, lesson plans, etc. Some may also contain textbooks and other course materials.
The following resources contain e-books that are free to access, but that don't necessarily allow modification and re-use unless there is a license stating otherwise.