Why not use your CiscoWorks installation? Current versions of CiscoWorks LMS come with a trial version of the Health and Utilization Monitor (HUM). CiscoWorks HUM monitors the device for performance parameters such as CPU utilization, memory utilization, interface utilization, interface availability, device availability and so on.
You could monitor these parameters and characteristics independently but would likely have to cobble together several tools to do so comprehensively.
Basic health,assuming logging is being done consistently can be monitored via syslog event analysis. An alternative to CiscoWorks' RME Syslog anayzer is the Kiwi syslog server (http://www.kiwisyslog.com/). Similarly one can monitor utilization statisitics with open source tools such as MRTG (http://oss.oetiker.ch/mrtg/), with CACTI graphing perhaps - http://www.cacti.net/ or third party licensed products such as Solarwinds Orion NPM (http://www.solarwinds.com/products/orion/). You can monitor configs with RANCID (open source - http://www.shrubbery.net/rancid/), etc.
Hope this helps.