[swombat]

Tweetmeme has been doing that for eons. You can even include it as a chicklet on your article, to encourage more retweets.

See, for example, http://tweetmeme.com/story/767267088/danieltennercom-how-to-...

[omakase]

BackTweets has actually been around for a while too -- and was always a part of BackType Connect (which shows you other reactions including hacker news, digg, reddit, friendfeed). We even personalize results to show a viewer which of their friends shared a link: http://www.backtype.com/connect/danieltenner.com%252fposts%2...

We have a similar chicklet to encourage retweets; it differs in that the colors are completely customizable and it integrates automatically with google analytics. Another one of our widgets shows only the interesting tweets: http://widgets.backtype.com/backtweets?url=http://danieltenn...