I have been working on deploying the latest version of the popular ntop bandwidth monitoring application. Here is a guide I wrote to get other started. I will make updates whenever I learn new things on this blog. You will also be able to download the latest copy of the guide from here.
I think ntop is a brilliant tool for seeing what is happening on your network in realtime. It is Open Source, Free [as in both free speech and free beer] and in active development. Check back on this page not ony for latest copy of documentation but also for some screenshots and use cases for ntop as well as other cool stuff I come across.