In response to increasingly burdensome textbook prices in higher education, many institutions and faculty are moving towards open textbooks as a way to control costs for students (for example, the Textbook Affordability Project at Temple). Open textbooks are freely available to download and use, and usually distributed under a copyright license that allows educators to share and remix content.
SUNY Geneseo offers OASIS, a search tool that simultaneously searches open content from 73 different sources.
Beyond textbooks: other Open Educational Resources include notes, syllabi, streaming video, and supplementary course materials. Here are some resources that help you identify open access (i.e., freely available) educational resources. For an overview, check out this primer on Open Educational Resources, including lists of resources and recommendations for incorporating OERs into your course.
Typically, purchasing eBooks is nearly as costly as buying a new copy of the print version. There are, however, quite a few resources on the open web where you can find free eBooks, particularly titles whose copyright has expired and now reside in the public domain.
HathiTrust - A partnership of academic and research institutions; offers a collection of millions of titles, most in public domain, digitized from libraries around the world.
Project Gutenberg - A digital library of free eBooks in the public domain. Most items are available to read online, as kindle files, and as EPUB files.
Bartleby - Publishes thousands of free online classics.
Archive.org - Offer over 8 million freely accessible eBooks.
Amazon*- Many public domain titles are available for free as Kindle or online reads. Try searching "free classics." You will need to sign in to an Amazon account to access these titles.
Google Books* - The world's most comprehensive database of digitized books, some of which have full-text access, and many of which have partial-text access.
(*While these can be great resources, please be aware that the quality of the digitized items can be poor.)