Books

Free for All
Full text of Peter Wayner's book, subtitled "How Linux and the Free Software Movement Undercut the High-Tech Titans". [PDF]
http://www.wayner.org/books/ffa/

The Linux Cookbook
All-encompassing book on using open source software, which itself is open source and available online.
http://dsl.org/cookbook/

Open Sources: Voices from the Open Source Revolution
The full text of this O'Reilly book has been made freely available online.
http://www.oreilly.com/catalog/opensources/book/toc.html

Perspectives on Free and Open Source Software
Book edited by Joseph Feller, Brian Fitzgerald, Scott A. Hissam and Karim R. Lakhani. Full text as PDF downloads of each chapter.
http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=11216

Producing Open Source Software - How to Run a Successful Free Software Project
Book by Karl Fogel. Full text freely available as HTML, PDF, and XML.
http://producingoss.com/