A Quarter Century of UnixPeter H. Salus256 pages published by Addison Wesley, 1994, ISBN 0-201-54777-5. This is a good review of the history of Unix with many interesting insights. Well worth a read if you are interested in where Unix came from and you can find a copy of the book.
The Cathedral and the Bazaar: Musings on Linux and Open Source by an Accidental RevolutionaryEric S. Raymond288 pages, published October 1999 by O'Reilly & Associates, ISBN 1565927249. Discusses the free software business model. The author is an identity in the Open Source movement and here captures a model of Open Source and Free Software development.
Linux in A Nutshell: A Desktop Quick Reference, Second EditionEllen Siever632 pages, published February 1999 by O'Reilly & Associates, ISBN 1565925858. An excellent reference to many standard GNU and Unix tools. An intermediate resource between this current book which aims to get you started with the tools and fully fledged manuals.
The Linux Sampler: A Linux Resource GuideBelinda Frazier and Laurie Tucker240 pages, published November 1994 by Specialized Systems Consultants, ISBN 0916151743. Presents an overview of Linux from the point of view of where, how, and why it is being used, with a little technical help thrown in.
Linux Rute User's Tutorial and ExpositionPaul Sheer500 pages, published January 2002 by Prentice Hall, ISBN 0130333514. Presents an excellent guide to many aspects of the Linux operating system. Also available from http://www.icon.co.za/~psheer/book/.