I know that MRTG has been mentioned but I am currently working with a similar issue.

I have 2 6500, 4 4006 and Nth 3548. I needed to monitor bandwidth, errors, etc.

I have Ciscoworks running which is pretty good, but I wanted a running history that a non-technical user good read. I found MRTG.

MRTG reads either MIBS vis SNMP and processes the data into a log file which is then processed as a graph and output is HTML. There is a quick and dirty configuration script which comes with MRTG that can be run with the IP address and community string. It gives out basic interface information.

MRTG can graph alot of other types of information like drive utilization, current users on a server or local director, CPU tempature on switches or CPU's, fan speed, and anything else that is available from a MIB.

MRTG can also be configured to read a log file. Suppose you are unable to use SNMP or the information you are looking for does not have a MIB? You can run a script that will gather the info you need and then have MRTG read that file.

The latest use I have for MRTG. I noticed that there was some strange looking traffic on my MRTG graphs of the Cisco PIX. (I monitor interface utilization all my PIX interfaces). I did not know who in my network was responsable. I set up MRTG to monitor and graph all active interfaces on all my switches. I was able to locate the offending system.