Check out the Many Eyes Data Visualization Tool.
Hear a keynote by the developers of Many Eyes, presented at the ‘Visualizing: From Data to Discovery’ symposium at Caltech:
Apart from the Many Eyes project, Fernanda Viégas and Martin Wattenberg have some really awesome visualizations! My 2 favourites:
Wind Map | http://hint.fm/wind/
Visualization of the History of Wikipedia entries | http://hint.fm/projects/historyflow/