Wordle is a site that lets you create word clouds from the text that you provide , think of a tag cloud in wordpress but with much more advanced and customizable features or simply word art online.
You can use the images that you have created for your blog , website header, tshirt or design. Just dont post it in the gallery section , since other users would have access to it, read the FAQ section for more details on using it commercially.
For now, you can edit the language, font , layout and color of your word art , but I hope they add new features in the future like, choosing shapes ( circles, stars, hearts , etc ) and different color schemes to changing individual text colors.
Visit the wordle site and try it for yourself.