I am going bonkers over server, process and network monitoring tools today. I guess it is because I often find it frustrating when services go down during the holidays. I have experienced a couple of problems before, when I was still the Director of the University Computer Center of the University of the Philippines. During my term, we had problems about the network going down due to power interruptions — one of our uplink was housed in one of the colleges in the university and the college admin decided to turn the power off for the holiday. :) Anyway, we've transferred that off of the building into somewhere we have access and control.
Anyway, like the tools that I have mentioned before, Nagios is another option, albeit more popular than Munin. Like Munin, it also supports plug-ins. Nagios also has the feature to alert administrators when there is something wrong with the services, server or network, either via e-mail, pager or even SMS. It even has a WAP interface. Nice, eh?
So if you are a system/network administrator, you have plenty of options to monitor your services. :)