Favstar.fm
Favstar.fm takes the concept of Twitter favourites to the next level making it quite meaningful by analyzing its popularity across the network.
As described on TechCrunch,
The main page shows a recent leaderboard that can be set to show tweets of only a certain level (10 favorites, for example). If you sign in via Twitter OAuth, you get a whole range of functionality, including the ability to follow people from Favstar.fm and see what tweets your friends are favoriting. Also, by signing in it is easy to see who is favoriting your tweets. As we all know, a big part of Twitter is vanity, so many of us likely want to know who is favoriting which tweets of ours. With Favstar.fm, it’s easy to see that.

Traffic rankings are sourced from multiple sources, if available, for the Twitter application. This includes Alexa, and Compete rankings.
July 13th, 2009 at 2:54 PM
Twitter Apps: Favstar.fm http://tinyurl.com/lud8oh