Tagxedo. What is Tagxedo? From the website:
Tagxedo turns words -- famous speeches, news articles, slogans and themes, even your love letters -- into a visually stunning tag cloud, words individually sized appropriately to highlight the frequencies of occurrence within the body of text.
I could see students taking a short piece of their writing and creating a tag cloud to see if any words are repeated too often. Or you can make a Tagxedo out of a tweet or a blog. A social studies lesson could come from entering the text of a famous speech. 101 Ways to Use Tagxedo will give you plenty of ideas on how to use this cool tool.