I don’t know if anybody else has already created one, but it seems almost too obvious and simple to not do it.
Super-simple install. Just download and un-gzip in your “wp-content/plugins” directory and enable it in the control panel. You can then add it like any other Wordpress widget. No configuration necessary (or possible).
You can see an example at right, under “Tagometer”.
For those of you who are old fashioned, you can also call the functions directly from your Wordpress templates to customize where the badge ends up.