I got an E-Mail this morning about the launch of a new site called MonitorForge. The sites focus is around the open source tools built for monitoring Servers and equipment. They are bragging about hosting 1700 projects. Some of note are the Nagios, Zenoss Core, Network Weather Map and MRTG. There are a lot of good tools out on this site. If you haven't tried any of these tools highly recommend you give at least a few a test run.