There are several word cloud generators out there, but lately I have been experimenting with Tagxedo. This generator allows you to make word clouds of websites, news stories, Twitter feeds and even web searches, then choose a shape for the cloud from tons of templates.
For created shaped clouds and using web sources, Tagxedo is much better than Wordle. If you intend to copy and paste text, however, Wordle is the better choice. Tagxedo currently does not have a field for entering text.
The United States Constitution
There are functions in Tagxedo for respinning, fonts, colors, shapes and even omitting words. Play with all of the functions and see what awesome images you can create. It's fun!