As everyone has stated, we use a custom bit.ly (http://rckstr.us/) as well as GaggleAMP.com (which provides advanced tracking and will tie to my Google Analytics to track performance). I also use ads.twitter.com to track raw performance of individual tweets.

A member of our Rockstar team, Steven Groves, co-author of The ROI of Social Media and a marketing measuring fiend, recommends additional reading from the respected publication TWN here: http://thenextweb.com/lifehacks/2013/10/08/want-to-create-your-own-url-shortener-heres-how-in-2013/

If you have further questions, you can reach me through Clarity.fm or on http://linkedin.com/in/loriruff or Steven Groves, ROI of Social Media: How to improve the return on your social marketing investment at http://www.socialmarketingconversations.com.