OER How-To at Guttman Community College

Open Textbook Library
The Open Textbook Library is a curated repository from the University of Minnesota which includes books that have been vetted/reviewed by faculty

OpenStax
OpenStacks is one of the leading providers of open textbooks. Their textbooks are well-respected, and are currently being used in 48% of college and universities in the U.S. OpenStax textbooks are free, open-source, peer-reviewed, and high-quality.  Most include test banks, slides, and other supplemental materials for faculty.

Math Textbooks from Lakeland Community College
Free and open pre-calculus materials