Many new sites have been added for the first time in September; our URL-Shortener index now includes a list of over 300 services. In this month's list you'll also find data on the amount of increase of activity that each site is seeing in September as compared to my last index published in July 2009.
A new feature of the index this month is the ability to click on the "Tweets per Day" number next to any URL Shortener, and view what links people are tweeting right now.
As an aside, Google just shipped a web commenting tool called SideWiki. They are currently getting 3,400 Tweets per day from SideWiki users (about 1/3 of the digg.com links). It will be interesting to see if SideWiki fades away, or garners more and more adoption.