Analytics: Three Keys to Building Your Author Platform by Dan Blank of WeGrowMedia.com explains how authors can use HootSuite, Tweetreach and other tools to measure their social media activity.
Tweetreach
9 Free Twitter Stats Analytics Services
9 Free Ways to Analyze Your Twitter Stats including Twittercounter, Tweetreach, Tweeteffect, Topsy, Tweetstats, Tweetalyzer, Tweetgrader, Backtweets and Owly