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...