tcptrack is a sniffer that displays information about TCP connections it
sees on a network interface. It passively watches for connections on the
network interface, keeps track of their state, and displays a list of
connections in a manner similar to the UNIX top(1) command. It displays
source and destination addresses, ports, connection state, idle time, and
bandwidth usage.

WWW: http://BSDforge.com/projects/net-mgmt/tcptrack/