NetMeter
Here is a great tool for you to monitor your network traffic with. Its called NetMeter and it obviously measures the amount of bandwidth in use.
It is stable and resource efficient. ( I like zoning out watching the little graph.)
The best use I have for this one is when traffic seems to go slowly, fire it up and see why. If your download is going at 30 kpbs but your NetMeter is showing 400 kbps, you have a serious problem. Its definitely the first line in your network defense troubleshooting.