Comments about oreilly Network Monitoring with Nagios:

If you have to setup Nagios the same day and have no clue yet were to start, than this is the text you need.

Just copy and paste the samples and you are good to go.

Once you got behind a certain stage chances are that you will want to extend on that knowledge. I do recommend Wolfgang Barths - System and Network Monitoring from No Starch (http://www.oreilly.com/catalog/1593270704/)

There is more out there http://www.amazon.com/Nagios-based-monitoring/lm/RWDDEA3CVS5VR/ref=cm_lm_byauthor_title_full/002-2752986-4323205

but No Starch Press's book is covering the most things.

Comments about oreilly Network Monitoring with Nagios:

Network Monitoring with Nagios is a good introduction to using Nagios in a small to mid sized network. It contains several configuration examples, and describes normal interaction with teh web interface.

I wish it had more coverage of creating new plugins, but I can see why that was left out of an introductory text.