cK-12 http://ck12.org/flexr/
Flatworld Knowledge http://www.flatworldknowledge.com/
Merlot http://www.merlot.org/merlot/index.htm
Connexions http://cnx.org/
Wikibooks http://en.wikibooks.org/wiki/Main_Page
OER Commons http://www.oercommons.org/
Open book Project http://openbookproject.net/
Community College Consortium for Open Educational Resources http://oerconsortium.org/discipline-specific/
Orange Grove Texts Plus http://www.theorangegrove.org/OGTtest.htm
Curriki http://www.curriki.org/xwiki/bin/view/Main/WebHome
Open Culture: http://www.openculture.com/free_textbooks
Textbook Revolution: http://www.textbookrevolution.org/index.php/Main_Page
MIT OpenCourseware: http://ocw.mit.edu/
Scribed: http://www.scribd.com/
DT - Digital Textbooks blog - http://digital-textbooks.blogspot.com/
Academic Earth http://academicearth.org/
Open Courseware Consortium http://www.ocwconsortium.org/
FolkSemantic http://www.folksemantic.com/
SOFIA http://sofia.fhda.edu/gallery/
Orangeware http://www.theorangegrove.org/OGMain.asp
Curriki http://www.curriki.org/xwiki/bin/view/Main/WebHome
Open Culture Free Courses http://www.openculture.com/freeonlinecourses
HippoCampus http://www.hippocampus.org/
Wisconsin ide@s http://www.ideas.wisconsin.edu/
Kahn Academy http://www.khanacademy.org/
VIDEOtalks http://videotalks.org/
Einztein http://www.einztein.com/
Open Course Library: http://www.opencourselibrary.org/
Open Educational Resources for California http://grou.ps/oercenter
Open Learning Initiative (carnegie Mellon) http://oli.web.cmu.edu/openlearning/index.php
iCommons http://icommons.org/
CliffsNotes: http://www.cliffsnotes.com/
SparkNotes: http://www.sparknotes.com/
Schmoop: http://www.shmoop.com/
GradeSaver: http://www.gradesaver.com/
Textbook Madness: http://textbookmadness.com/
Get Textbooks: http://www.gettextbooks.com/
Chegg: http://www.chegg.com/