Amazon.com just posted my two reviews on books about Nagios. The first is Pro Nagios 2.0 by James Turnbull. Here is a link to the five star review.
The second is Nagios: System and Network Administration by Wolfgang Barth. Here is a link to the four star review.
Both reviews share the same introduction.
I recently received review copies of Pro Nagios 2.0 (PN2) by James Turnbull and Nagios: System and Network Monitoring (NSANM) by Wolfgang Barth. I read PN2 first, then NSANM. Both are excellent books, but I expect potential readers want to know which is best for them. The following is a radical simplification, and I could honestly recommend readers buy either (or both) books. If you are completely new to Nagios and want a very well-organized introduction, I recommend PN2. If you are somewhat familiar with Nagios and want detailed descriptions of a wide variety of Nagios plug-ins, I recommend NSANM.