Twitterholic

http://twitterholic.com/

"Our twittastic robots scan the Twitter public timeline for new twits to tweet. A few times a day, we calculate individual statistics for each twittering twit in our database."

So anyway basically this site can show you who the currently most followed 'Twitts' are, where they're from and other stuff.

Barack and Britney are both up there with the top rankers - I'm not actually listed myself although I've only ever 'twittered' the one time so it's hardly surprising eh.