Are you a fan of Wordle? This iOS app lets you create word collages easily, without having to move to a desktop machine.
"Create stunning word collages on your iPhone and iPad! Set up a collage with your text(or website URL), different layouts, fonts, and color themes. Simply start by clicking on the "Text" button. Add some text or input a website url. Select color theme and font in Settings. Select Landscape or Portrait orientation. Word Collage even lets you pan and zoom the picture."