I've been very happy with Scout (http://scoutapp.com/ http://scoutapp.com/) for monitoring. It's a nice mix of standard monitoring and a pretty simple plugin sy

I've been very happy with Scout (http://scoutapp.com/ http://scoutapp.com/) for monitoring. It's a nice mix of standard monitoring and a pretty simple plugin system for custom monitoring. All of the plugins are written in Ruby and the interface for reporting data is pretty simple. I'm using it for everything from monitoring the KB/s that systems are swapping (and alert if it's anything measurable) as well as custom things like job queue depths.