[linker3000]

...and some use Centreon, which bolts graphing and a better UI onto Nagios 'out of the box'

http://www.centreon.com/ ..or install via FAN: http://www.fullyautomatednagios.org/wordpress/

[kudu]

It isn't very clear to me which Nagios plug-ins are considered standard, and perhaps that sort of confusion is what creates all the FUD surrounding Nagios.