There’s a really neat post over at Tutorialzine on how to build A Twitter List Powered Fan Page.
It’s a little widget, that would go in your sidebar or some similar place, where it would display the Twitter avatars of anyone who wanted to click a button to add themselves to a Twitter List (along with an overall count of the “fans”).
It seems like a neat idea, though you have to do a bit of PHP and JavaScript work to get it up an running. (It would be nice to see a variation made as a WordPress plugin…)