My Fave: Tagxedo
(this is an example of my Twitter stream vasimpleservice using Tagxedo)
Tagxedo turns words — famous speeches, news articles, slogans and themes, even your love letters — into a visually stunning word cloud, words individually sized appropriately to highlight the frequencies of occurrence within the body of text.
Check out 101 ways to use Tagxedo
Find out more on Tagxedo.com