http://www.hetos.de/bwlog.html

That is a nice utility that runs in the router itself. It states that it is for DD-WRT, but it works well with Thibor's latest firmware. Note that the latest hardware revisions for the G and GS don't run Linux, so it won't work. The GL runs Linux, period.

I just measured the bandwidth usage while talking on the phone with Vonage, and it was around 10.1K/second.

Those who have metered bandwidth will find the utility especially useful. I am using it to check bandwidth usage while hosting online games, and to see my real download/upload from web pages at the router itself.