WatchWAN is a more accurate alternative to DU Meter, Netmeter and other bandwidth monitors.
Unlike others, it allows you to set filters to capture only the traffic you are interested in.

It shows all the active connections you have to the Internet at any given moment and also the
volume of traffic flowing through them.
Ofcourse, keeps an exact record of your bandwidth usage too.
Has a simple no-nonsense interface.
Planned to be GPL'ed