Good overview of the best way I've seen to use Nagios.

Walkthrough of how one would derive Nagios alerts from Graphite graphs. The explanation doesn't match up with the implementation: it claims to use some bleeding-edge feature of Graphite but in reality if just downloads the graph and attaches it to the email.

MCollective-alive over RabbitMQ that's focused on monitoring. Might be worth a second look for the Nagios forwarding alone.

Next-generation NSCA-alike for pushing checks to the Nagios server rather than having it poll.

APIs to Nagios.

A likewise comprehensive list of Nagios-focused interoperability tools.

Ruby code for describing a Graphite graph. So far, this appears to be used to drive Nagios checks based on data collected by Graphite.

Full list of Nagios macros.

On-demand NRPE runs.

Docs for the Swiss army knife of Nagios.

Pythonic way to make writing Nagios plugins bearable. Puppet should be able to take it from here to make the end-to-end easy.