A great little application that runs in a shell prompt to let you know which applications are eating your bandwidth – live.
sudo apt-get install nethogs
Then run . . .
. . . from your shell prompt and enjoy the detailed information!
One odd caveat though: I had a Windows virtual machine running under Virtualbox that was using about 150Kbps and NetHogs did not list it by application, instead it listed it by IP address – in this case, the IP address of the virtual machine along with source and destination port numbers. It also did not attribute the traffic to eth0, but left the device blank.
I was expecting it to list the application, but I suppose in some scenarios (especially virtualization) all the available information may not be immediately available to NetHogs and so it will simply default to source/destination IP & port number.