Wordle.net is a tool that can be used to create "word clouds." You provide the site with a list of words and the words that are listed most frequently appear largest in a collage of the provided text. This can be custom made with numerous colors, fonts, and layouts.
Wordle is excellent and has been around a while - as have some other word cloud generators.
My own bookmarked links here
There is another great word cloud site that you should check out. Tagxedo.com allows you to incorporate your words into images. We use this at Pace University (New York) for students to use on their e-Portfolios (online, electronic portfolios).