OpenStax is a nonprofit based at Rice University that has published more than 20 open source, peer-reviewed, textbooks in different subjects for undergraduate students.
Online Textbooks - MIT OpenCourseWare
Some of these online textbooks are open-licensed electronic versions of print books. Others are self-published online books, or course notes which are so thorough that they serve as an alternative to a conventional textbook.
Open Textbook Library - University of Minnesota
The Open Textbook Library provides a growing catalog of free, peer-reviewed, and openly-licensed textbooks housed at the University of Minnesota and sponsored by the Open Textbook Network.
A repository of over 50,000 educational resources for all levels.
A project that provides funding and support to faculty members in the State University of New York who wish to publish open textbooks. Over a dozen textbooks have been published to date with more forthcoming.
British Columbia Ministry of Advanced Education’s Open Textbook Project makes open textbooks available in BC's 40 highest-enrolled academic subject areas.
Open textbooks by the University of South Florida.
Open Textbook Initiative by the American Institute of Mathematics
The American Institute of Mathematics offers a collection of Mathematics textbooks for different courses.
Download a list of suggested textbooks that are relevant to certain courses taught at AUK