Debian (and consequently Ubuntu) contains a range of extraordinarily useful monitoring packages.
I've been maintaining several of them at a basic level but as more of my time is taken up by free Real-Time Communications software, I haven't been able to follow the latest upstream releases for all of the other packages I maintain. The versions we are distributing now still serve their purpose well, but as some people would like newer versions, I don't want to stand in the way.
Monitoring packages are for everyone. Even if you are a single user or developer with a single desktop or laptop and no servers, you may still find some of these packages useful.
For example, after doing an apt-get upgrade or dist-upgrade, it can be extremely beneficial to look at your logs in LogAnalyzer with all the errors and warnings colour-coded so you can see at a glance whether your upgrade broke anything. If you are testing new software before a release or trying to troubleshoot erratic behavior, this type of colour-coded feedback can also help you focus on possible problems without the eyestrain of tailing a logfile.
A good first step is simply looking over the packages maintained by the pkg-monitoring group and discovering whether any of them are useful for your own needs.
You may be familiar with alternatives that exist in Debian, if so, feel free to comment on whether you believe any of these packages should be dropped by cre ating a wishlist bug against the package concerned.
The next step is joining the pkg-monitoring mailing list. If you are a Debian Developer or Debian Maintainer with upload rights already, you can join the group on alioth. If you are not at that level yet, you are still very welcome to test new versions of the packages and upload them on mentors.debian.net and then join the mentors mailing list to look for a member of the community who can help review your work and sponsor an upload for you.
Each of the packages should have a README.source file in the repository explaining more about how the package is maintained. Familiarity with Git is essential. Note that all of the packages keep their debian/* artifacts in a branch called debian/sid while the master branch tracks the upstream repository.
You can clone the Debian package repositories for any of these projects from alioth and build them yourself, try building packages of new upstream versions and try to investigate any of the bug reports submitted to Debian. Some of the bugs may have already been fixed by upstream changes and can be marked appropriately.
Two particular packages I would like to highlight are ganglia-nagios-bridge and syslog-nagios-bridge. They are not exclusively for Nagios and could also be used with Icinga or other monitoring dashboards. The key benefit of these packages is that all the alerting is consolidated in a single platform, Nagios, which is able to display them in a colour-coded dashboard and intelligently send notifications to people in a manner that is fully configurable. If you haven't integrated your monitoring systems already, these projects provide a simple and lightweight way to start doing so.