The B.C. Open Textbook Project is funded by the BC Ministry of Advanced Education. A goal of the Project is to provide flexible and affordable access to higher education resources by making available openly-licensed textbooks. Textbooks are available for Applied Science, Biology, Chemistry, Computer Science, Earth Sciences, Engineering, Maths, Statistics, and Physics.
College Open Textbooks is NOT a content provider. Instead, they search available open textbooks and provide the links. Currently, they are tracking more than 100 open textbooks for use in community college courses.
The Global Text Project is a joint project of the Terry College of Business of the University of Georgia and The Daniels College of Business of the University of Denver. It aims to publish electronic texts for students in the developing world and maintains a database of links to books for such students.
The National Academies Press (NAP) was created by the US National Academy of Sciences to publish the reports of the National Academies of Sciences, Engineering and Medicine, operating under a charter granted by the Congress of the United States. The NAP publishes more than 200 books a year on a wide range of topics in science, engineering, and medicine, providing authoritative information on important matters in science and health policy. They offer more than 8,500 titles in PDF format. Almost all of these PDFs can be downloaded for free by the chapter or the entire book (Source: NAP webpage). Subjects covered include Biology and Life Sciences, Computers and Information Technology, Earth Sciences, Energy and Energy Conservation, Engineering and Technology, Environment and Environmental Studies, Math, Chemistry and Physics, Policy, Space and Aeronautics, Surveys and Statistics, and Transport and Infrastructure.
Open Textbook Library (OTL) provides textbooks that have been funded, published, and licensed to be freely used, adapted, and distributed. These books have been reviewed by faculty from a variety of colleges and universities to assess their quality. They can be downloaded for no cost, or printed at low cost. All textbooks are either used at multiple higher education institutions; or affiliated with an institution, scholarly society, or professional organization. Subjects covered include Computer Science & Information Systems, Engineering, Mathematics, and Natural Sciences.
Wikibooks is a collection of open-content textbooks, a Wikimedia project for collaboratively writing open-content textbooks that anyone can get edit right. Wikibooks includes textbooks, annotated texts, instructional guides, and manuals. These materials can be used in a traditional classroom, an accredited or respected institution, a home-school environment, as part of a Wikiversity course, or for self-learning. Subjects covered include Computing, Science, Mathematics, and Engineering.
MIT OpenCourseWare (OCW) is a web-based publication of virtually all MIT course content. OCW is open and available to the world and is a permanent MIT activity. Course content is available from the School of Engineering and the School of Science.
Access a range of course materials, videos, lectures, student work and more. Nearly all of the content here is openly licensed for reuse under Creative Commons. Resources are available for subjects including Chemistry, Engineering, Mathematics, Physics, and Statistics.
The BCcampus Open Education Self-Publishing Guide is a reference tool for those wanting to write and self-publish an open textbook. It provides details on the preparation, planning, writing, publication, and maintenance of an open textbook. Copyright, open-copyright licences, and the differences between citation and attribution are discussed as well as the importance of copy editing and proofreading. Checklists and templates are also provided. This guide replaces the BCcampus Open Education Authoring Guide.
These are useful websites and OER portals, that in some instances allow you to search by education level and by material type eg video, lesson plan.