Despite an increase of over 200 pages, the book cannot describe all the existing tools and possibilities for use. The Internet provides a wealth of information that is useful while, or after, studying this book. The most important sources are listed here.
The Nagios homepage at http://www.nagios.org/
The homepage of Nagios plugins at http://www.nagiosplugins.org/
The Nagios community at http://www.nagioscommunity.org/
http://www.nagiosexchange.org/ as an exchange platform for plug-ins
The original mailing lists at http://www.nagios.org/support/mailinglists.php