The hardest part of being a solo administrator is watching a system during your down time. There are a few monitoring tools out there but I needed a quick, and preferably easy one to set up.
OpManager has a free version for up to 10 nodes so I have recently installed it on one of my home PC's and have been testing it the last week.
I must say, it has a lot of nice tools. The GUI uses your browser calling off a local server it installs on your PC. In my experience it connects to the servers it monitors using a hybrid approach between SNMP and SSH. It grabs a bunch of the normal statistics but where I found it most useful was the alarms and notifications. I can have it notify me by SMS (it emails my phone) and also by email when the server or a specific service becomes unresponsive.
It has many features I have yet to even try, but so far I am liking it way better than WebCacti!