network traffic monitor on a per-app basis?

[benit]

I am sorry... now I know what you mean. Of course I know this widget! I was referring to any application that would allow me to monitor the network traffic by application / process so that I can figure out which application / process is contributing how much to my overall network traffic.

I hope you have a hint for me for this, too. Any user friendly app is ok for me, hopefully GUI, but not a must.