Accurate Network Monitor attaches itself to the TCP/IP driver and monitors all incoming and outgoing network traffic. It captures all packets the operating system components and applications send and receive via the IP protocols family (including, but not limited to TCP/IP and UDP/IP). All source and destination endpoints are automatically resolved, giving you the exact knowledge of the communication channel properties.
it looks really good to me, but i can't work out if it's shareware or freeware, or if there's two versions. at BetaNews it says freeware, but if you go to the site it has a Buy Now link as well as Download Now.