Cisco's CiscoWorks management suite is be a great tool for those that can afford it. For the rest of us, however, it's overpriced and overcomplicated for day-to-day administration tasks. There isn't really a lower-level tool provided by Cisco for managing medium to large Cisco-centric infrastructures. Enter NeDi.
Remo Rickli started NeDi several years ago as a small collection of Perl scripts designed to query Cisco devices for relevant data. It's grown into a very useful network management tool that provides a very simple way to identify and track hosts across a large switched and/or routed network. It still consists of a collection of Perl scripts, but the collection has grown substantially.
Currently, the 1.0 release of NeDi is waiting in the wings. When I first stumbled on this project over a year ago, I was drawn to the simplicity and strict elegance of the solution. A cronjob runs every 3 or so hours, pulling the forwarding table from switches, routers, and wireless access points across the network. New devices are discovered via CDP and added to the query list automatically, so only a seed device need be specified to get the ball rolling. Once that data is collected, the Web-based front end allows searches to be made on nearly every aspect of a client --- MAC address, IP address, NIC type, and so forth. This way, it's simple to determine where a host physically exists on the network, what the I/O and error counters are for the switchport connected to that host, and even NetBIOS queries against that host to determine OS, current user and more.
There are other functions as well, such as the ability to archive device configurations and search devices for specific config elements, as well as switch population tracking, hub detection, node reports, stock tracking, and so on. There's even a facility to push configurations to network devices. While NeDi is certainly Cisco-centric, there is support for HP ProCurve switches as well, since they support the CDP discovery protocol.
Back when I first discovered NeDi, it was running with a flat-file database. I had a client that could really use the tools provided by NeDi, but the size of the network really required more than a flat-file backend. So armed only with my trusty PowerBook and a cross-country flight, I rewrote the NeDi backend to use MySQL, and contributed the code back to Remo. It's taken awhile to fully incorporate the changes and add significant new discovery and layout features to the code, but NeDi 1.0 should be released soon with MySQL support as well as a slew of new backend and frontend code.
If you run a Cisco network, it's definitely worth your time to investigate this tool. It's a great example of open source software nicely filling in the gap.