Wordle

http://www.wordle.net/

A tag cloud or word cloud (or weighted list in visual design) is a visual depiction of user-generated tags, or simply the word content of a site, typically used to describe the content of web sites. Tags are usually single words and are normally listed alphabetically, and the importance of a tag is shown with font size or color.^[1] Thus, both finding a tag by alphabet and by popularity is possible. The tags are usually hyperlinks that lead to a collection of items that are associated with a tag.