Ever been frustrated that an ebook was not freely available?
Well, join unglue.it. At unglue.it, you can make a pledge that will go toward making traditionally published books freely available online.
Open Textbook Catalog (online version is free. From University of Minnesota)
SmARThistory (Art History textbook provided by Khan Academy)
Student PIRGs: Open Textbooks (catalog of open textbooks)
Wikibooks (anyone can edit)