From the good folks at George Mason University, you can use this to search across multiple OER sites.
To promote the use of OER on their campuses, more college and university libraries are starting "Alternate Textbook Projects". These projects encourage faculty to replace their commercial textbooks with alternate resources such as OER and licensed library content (which is openly available to all the members of that institution). This section of the Guide will link you to several of these programs.
If this is your first foray into developing Open Education Resources it can seem overwhelming. Your liaisons are here to help!
If you just want to get a sense of what is available, browse these three sites:
NOTE: There is a lot more out there. If you are interested in developing/searching for resources, your liaison is happy to partner with you.
Other resources that may have materials you can use for your class. Some of these are more specific to certain fields.
Other Tools that might be helpful.
See how one library supports faculty as they develop OERs. Our library is also willing to help as you develop and seek resources for your courses.