Wordle is a toy for generating “word clouds” from text that you provide. The clouds give greater prominence to words that appear more frequently in the source text. You can tweak your clouds with different fonts, layouts, and color schemes.
I had a play with it using the text from the Wikipedia page about Visualization (http://en.wikipedia.org/wiki/Visualization_(graphic)):
It was fun to play with the presentation options, and the results are decorative, but I’m not sure how useful they are in conveying information.