We recently did a search for some good network monitoring software. It wasn’t specifically required by the SAS 70 audit, but it has greatly helped us in monitoring server/application availability as well as getting notified of outages or other events (disks nearing capacity, etc).
We looked around and there were several solutions out there, but ultimately we decided to go with Zenoss. It was open source and the free edition had all of the features we were looking for. It can perform all sorts of different monitoring and make use of things like SNMP and even use existing Nagios tests.
We’re still playing with some of the tests and trying to figure out some good indicators of issues that we can set notifications on, but all in all, it was a very simple setup and configuration. I would definitely recommend this product to anyone that wants to be able to monitor availability and performance on their network.