Port Explorer - Port Explorer allows you to see all the open network ports/sockets on your system and which programs own them. Along with this ability it also has many tools including a packet sniffer, bandwidth throttling and country detection to name just a few.
Fast Port Scanner - Scans about 400 ports a second. It supports both the TCP/IP and UDP protocols. Select address ranges to scan multiple interfaces or hosts. Open ports will found will have suspected trojans listed. Free for website monitoring service clients.