We Need a “Fan” button for our site…

We have a Fan site where users can create a website related to something or someone they are a fan of. It’s a 3.0 multi-site enabled site.

We are looking for a simple plugin that would allow users to click on a button, something like “Become a Fan” or something like that. This would register on a visible total like “222 Fans”. The new “Fan” would be required to be logged in to become a fan. If they are not logged in, then a message will appear with an explanation and a register button.

I’m strictly talking about being a fan of the site/blog, not a particular post.

Any plugins out there like this? (I’ve seen some related to facebook, myspace, etc., but don’t want that. This is only for internal use on our site.)

Thanks!