NagiosExchange hosts a large number of third-party plugins under the Check Plugins, Software, SNMP category (visit http://www.nagiosexchange.org/ cgi-bin/page.cgi?g=Check_Plugins/Software/SNMP/index.htm). These allow the monitoring of the system load over SNMP, the monitoring of processes, and storage space, and the performance of many other types of checks. You can also find checks that are dedicated to specific hardware, such as Cisco or Nortel routers. There are also plugins for monitoring bandwidth usage.

There are also dedicated SNMP-based check plugins that allow the monitoring of many aspects of Microsoft Windows, without installing dedicated Nagios agents on these machines. This include checks for IIS web server, checking whether WINS and DHCP processes are running, and so on.

The Manubulon site (http://nagios.manubulon.com/) also offers a very wide variety of SNMP plugins. These offer checks for specific processes that are running, monitoring the system load, CPU...