FTOTW is the WordPress Plugin that powers http://www.sastwingees.org/ftotw/
It fetches retweets from Twitter and adds them to WordPress DB, after assigning a score to each of them. The retrieved tweets are used to create a weekly post about the most interesting tweets that were retweeted. The Plugin also creates a leaderboard which displays the twitter users with the highest score.
Note: Kindly note that this Plugin is heavily customized for http://www.sastwingees.org/ and may not be suitable for you, if you are not comfortable looking into the code.
This Plugin is released under GPL.