Show data send and read at a given port.
Parses output intelligently somewhat like Wireshark to make it easier to read.
http://superuser.com/questions/23180/whats-the-easiest-way-to-sniff-tcp-traffic-data-on-linux
Ubuntu 12.04 install:
sudo aptitude install tcpflow
Sample usage:
sudo tcpflow -i any -C -e port 1234