I just read about Twittervision--on Twitter, of course. It's a cool Twitter/Google Maps mashup that constantly displays recently posted Twitter updates, located on a world map. It's a peek into the stream of consciousness of the Twittersphere. Robert Scoble thinks "memes are going to go nuclear with Twitter," and that this tool will help.
With some additional development, I can certainly see that happening. The site has only been live for a few hours, so I don't want to criticize it, but I do hope that the developer, David Troy, adds some filtering capabilities. It would be nice if you could just watch friends' Twitters, for example, or if you could get a live map view only of Twitter messages that contain certain keywords.
Troy has also created Twittermap, which shows the location of Twitter messages based on your search term (not real time, like Twittervision), and Twittersearch, which is a Twitter archive search engine.