Rancid - Really Awesome New Cisco ConfIg Differ
An article - http://www.networkcomputing.com/showitem.jhtml?docid=1614ws1
The tool - http://www.shrubbery.net/rancid/
A slough of other general network/monitoring stuff
Nagios -I haven't put the product into production yet, but I know a few who have and it looks promising. It is a free monitoring server that can do a fair amount although a lot of IT departments don't like it because it is harder for them to setup than MOM(which is a pretty nice product but CALs can kill ya)
http://www.nagios.org/about/
There are some others, but I can't recall them right now. I have a ton of these bookmarked if anyone is looking for a specific type of software.