The links below are open resources mega sites that offer books as well as other OER teaching tools.
Assayer Largest catalogue of open sources textbooks. Also is a good place to find free books about math, science and computers.
• AU Press Athabasca University Pree - free pdf and low cost print version of mainly Canadian books.
• BC Campus OER BC Campus open movement including textbooks.
• BCcampus SOL*R - Shareable Online Learning Resources Shareable, browseable and searchable open resources
• Boundless Boundless has high quality content and resources build by a community of educators and experts. It provides ready-to-use content, tools, and test materials
• College Open Textbooks Lists open textbooks by subjects, many of which are peer reviewed.
• Community College Consortium for Open Educational Resources Advocacy, training, and links to college level open textbooks and other courseware.
• Connexions Content Commons of free, open-licensed educational materials in fields such as music, electrical engineering and psychology.
• Global Text Project "We publish open content electronic textbooks that are freely available from this website. We focus on content development and Web distribution, and we will work with relevant authorities to facilitate dissemination by other means when bandwidth is unavailable or inadequate. The goal is to make textbooks available to the many who cannot afford them."
• HathiTrust Digital Library HathiTrust is a partnership of major research institutions and libraries and their "aim to build a comprehensive archive of published literature from around the world . It provides long-term preservation and access services for public domain and in copyright content from a variety of sources, including Google, the Internet Archive, Microsoft, and in-house partner institution initiatives."
• Knowledge Unlatched "The Knowledge Unlatched model depends on many libraries from around the world sharing the payment of a single Title Fee to a publisher, in return for a book being made available on a Creative Commons licence via OAPEN and HathiTrust as a fully downloadable PDF."
• Merlot Free and open resource designed primarily for higher education.
• National Science Digital Library Access to teaching and learning materials in the STEM disciplines (science, technology, engineering and mathematics). Search by level, resource type, and subject.
• OER Commons Worldwide learning network of shared teaching and learning materials.
• Open Courseware Consortium Collaboration of higher education institutions to share and expand their open course offerings.
• OpenStax College
• Open SUNY Textbooks "Open SUNY Textbooks is an open access textbook publishing initiative established by State University of New York libraries and supported by SUNY Innovative Instruction Technology Grants".
• Open Textbook Library One of the larger repositories of open textbooks. Includes selections from BCcamous, Calpoly and many more.
• Orange Grove Text Florida's operational repository project of open source educational materials.
• Saylor Free Education Free to read versions of the texts at Flat World Knowledge
• Textbook Revolution "Textbook Revolution is a student-run site dedicated to increasing the use of free educational materials by teachers and professors. We want to get these materials into classrooms. On this site you'll find links and reviews of textbooks and select educational resources."
• Wikibooks Wikimedia's community for creating and sharing educational textbooks.