#1. Best bet: Try the OER by Subject page from OASIS, sponsored by SUNY-Geneseo. All sources listed here are fully open.
#2. Try the Open Educational Resources by Subject Disciplines guide from Washtenaw Community College – Bailey Library.
#3 Try the No Cost Tittle List guide from Citrus College--Bailey Memorial Library (distinguishes between OER and library sources that are no cost to students)
#4. Try the OER by Subject Area guide from Tidewater Community College