MyWanIp

From Tzolkin:

MyWanIp is a Windows utility that allows you to discover your WAN IP address. Many home- and small-business users have broadband routers, like the Linksys Etherfast Cable/DSL Router, SMC, Nexland, Netgear Series, and others between their LAN and their Internet connection. When a LAN PC is connected behind one of these routers, most IP Address utilities will only tell you the LAN IP address.

This is not useful to someone trying to connect to your router or your computer from the Internet. MyWanIP always displays the proper WAN IP Address, the true IP address needed to connect to any PC on the LAN. MyWanIP uses remote servers to determine the Cable/DSL router's true WAN IP address, and shows that IP address in a small window. This allows you to determine the IP address that someone else needs to connect to your computer over the Internet.