O'Reilly is making a number of its computer books available for free, under a concept they call 'Open Books'. These books are out of print or the author has requested that they be distributed for free. All the books are being published under what they call an 'open' copyright.
O'Reilly has partnered with Creative Commons and the Internet Archive, to address the licensing and digitizing challenges involved in bringing the Open Books to readers. They have also adopted the Creative Commons Founders' Copyright, which they're applying to hundreds of titles pending the author's approval.