Free and Reduced Cost Textbooks and Learning Content

Akademos Textbook Adoption Tool: Find and compare textbooks across 3,600 subjects and 2 million books. 

BookBoon: offers over 1,500 ebooks in seven languages, directly available for download from the website. This company's collection is strongest in the fields of business, engineering and math. 
 An open educational resource aggregator. It brings together free resources on the web to match the content of your existing textbook. Its offerings are limited but are entirely free and the interface is very easy to use.

College Open Textbooks by Subject

Directory of Open Access Books: A collection of over 700 open access, peer-reviewed books in a variety of disciplines.

Free Textbook Lookup Tool: CSU's Affordable Learning Solutions' Free Textbook Lookup Tool lets you enter the ISBN of a textbook to find related FREE open textbooks.

MERLOT (Multimedia Educational Resource for Teaching and Learning) Peer reviewed online teaching and learning materials. 

OpenStax College: Funded by several non-profit organizations including the Hewlett and Gates Foundation and provides free, digital textbooks for Physics and Sociology.

Open Academics: 
Created by the University of Minnesota, Open Academics is a catalog of open textbooks reviewed by faculty members. All textbooks include a print option, generally for $40 or less.

Open Courseware Consortium: A collaboration of higher education institutions and associated organizations from around the world. It provides a collection of open educational content using a shared model.

Open Educational Resources Center for California: Designed for community college educators, the OER Center for California provides resources for finding, creating, remixing, using and sharing openly licensed learning content. 

Open Library
:  The Open Library provides access to over one million fiction and non-fiction titles, all online and available for free. 

The Orange Grove:  An online library of openly available instructional resources created for Florida's colleges and universities.

PLoS (The Public Library of Science) open-access articles and journals in the areas of science and medicine.

Textbook Revolution: A student-run site dedicated to increasing the use of free educational materials by teachers and professors.