iftop: iftop (display bandwidth usage on an interface)
iftop:
iftop: iftop does for network usage what top(1) does for CPU usage. It
iftop: listens to network traffic on a named interface and displays a table
iftop: of current bandwidth usage by pairs of hosts. Handy for answering the
iftop: question "why is our ADSL link so slow?"
iftop: 
iftop: You will need the libpcap and ncurses packages to be installed in 
iftop: order to use iftop.
iftop: Homepage: http://www.ex-parrot.com/~pdw/iftop/
iftop: