Like the open source movement in software, an open source movements in the textbooks may be afoot. If this movement takes hold it will surely impact the textbook business, which is perhaps the only safe island in a sea of troubled publishing business.
The other question is what motivates people like Professor R. Preston McAfee to make their books available for free, when they could have earned a fair bit from it – $100,000 advance and more, according to a New York Times article (Don’t Buy That Textbook, Download It Free)
Some sources for free textbooks:
Free Learning http://freelearning.bccampus.ca/
MIT OpenCourseWare http://ocw.mit.edu/
Open Textbook http://opentextbook.org/
Google’s Free Textbook Search http://www.freetextbooks.eu/
Please feel free to add to the list if you know of any more.