Show your IP Address in the Menu Bar
Do you need your IP address often? If so, IPMenulet is likely the quickest way to have the number handy all the time, it’s a free and simple menu item that displays your current external IP address in the Mac OS X menu bar, there’s no other frills or features.
Little utilities like this are really useful if you have a dynamic IP or just find yourself frequently moving around to different networks, although if you fall into the second category and need to allow local connections, you’d probably benefit from using a service like DynDNS, but that’s another topic.
You can always find your IP address in Mac OS X through System Preferences, using the command line, or accessing a web site like whatismyip.org too.