Bandwidth and Usage Monitoring

Check out M. Bilal's howto on Bandwidth Monitoring Free & Paid Tools Software Details.
http://community.spiceworks.com/how_to/show/2532

Two useful, free products from Solarwinds:
Real-Time Bandwidth Monitor
http://www.solarwinds.com/products/freetools/real-time-bandwidth-monitor.aspx

Real-Time Netflow Analyzer
http://www.solarwinds.com/products/freetools/netflow-analyzer.aspx

Bandwidth monitoring works well to watch specific interfaces on routers (the WAN router might be interesting, for example). When it comes down to tracking what devices are conversing with local and internet locations, Netflow is the correct tool. The free tools work well as long as you don't need historical data. If you need to track down what happened last night, then the paid versions are what you're looking for.

http://community.spiceworks.com/pages/solarwinds