The tool has a ton of already-loaded photos with search capacity, or you can upload your own. Type in what you want to say, select a typeface (there are presently nine), and move the text around in the image. The final step is to download, post to Facebook, or Tweet. Oh, and before you post, you get a preview.
And all for free with no sign-up or log-in required. (This may actually be the best part!)