I've bookmarked several tag cloud implemetations for future use myself. If you know of an open source control please post a link. Keep in mind that we can't use anything under the GPL license, but most other OSI approved licenses are ok.
It might be possible to use this in the blog at the moment, but before it can be used more widely in the site I have to implement some core plumbing that features can leverage for tagging. I've got some design work started on it but not sure when it will move to the top of my stack.