A preview of Twittier.com is available.
On receiving a message it extracts "relevant" keywords and displays a "live cloud view" of keywords. This cloud view is updating in real time, and thus gives you an idea of the trending topics on twitter at any given time.
At the moment it doesn't work on IE6, though I haven't tested IE7. I'm developing this on Firefox3 beta but Firefox2.0 should display it fine also.