This website generates word clouds from a text or feed that you provide. The size of the words in each cloud will depend on the frequency in which they are used in the text. You can select between several fonts, colors and layouts for every graphic generated.
Wordle from paletadelimon.wordpress.com:
Wordle made out of several words:
Wordle from www.good.is:
There are hundreds of options, do yow want to try? Here.