wminet is a very useful dock app for monitoring internet connections to and from your computer.
The number of connections can be filtered based on local and remote addresses and ports, on either tcp or udp. It can also display hostname and number of processes.
This new version uses a lot less CPU and allows greater configuration. The original program can be found here. However, I have removed the ability to monitor httpd and ftpd processes, nfs mounts and lpd queues.