I've uploaded a new web tool to RomSteady.net. "What IP?" tells you what external IP address is being reported for your machine.
Given how often I need to know what IP address I'm coming from, I'm amazed something like this hasn't popped up before...
Update 10/10/05, 1:53pm: After viewing some of the alternatives listed in the comments, I've decided to keep the tool up. It's still one of the smallest pages (byte-wise after total load) out of the multitudes out there, and one that doesn't use pop-up, pop-under or Flash-overlay ads to subsidize it.
That being said, I want to make it more useful, so I'm going to put up an XML Web Service API for it tonight that will let you retrieve all of that information from a client application. I'm also going to add in some components that are currently missing.