I use MRTG to watch router traffic and dial-in usage on Amigo.Net's Portmasters. It's very easy to setup but could be easier for others in the company, i.e. not me, to add things to the system for monitoring. I created a very simplistic web-based app for adding routers, portmasters and servers to the system. I have the portmaster modules for that in the scripts directory. One of these days, I'll put the whole app up. (Then again, maybe not since I'm working on a new version based on rrdtool.)