Tagxedo does Wordle one better, allowing users to apply shapes to their word clouds. Here, I've put the Gettysburg Address into a dove shape (the quotation balloon shape didn't look very good). It includes all the usual tools for designing your cloud--color, orientation, etc.
In addition, Tagxedo has kind of a cool feature when it's online. Hover your pointer over a word, and it "pops up," highlighted. Good for concept discussion. In its current Beta version, it even allows you to upload your own shape, though it looks like that will become a pro feature eventually.