Have You Ever Wonder Who Unfollowed You on Twitter?
who.unfollowed.me is a great site that allows you to track who unfollows you on Twitter. Some of the unfollowers will come as a surprise to you, and some of them will not. In any case feel free to reciprocate the gesture or not.
who.unfollowed.me has a free option as well as a paid option.
Both options begin with signing into who.unfollowed.me with your Twitter account. You are then asked to give the website the authority to access your Twitter account. Upon given authorization, who.unfollowed.me will get to work on detecting all of your followers. The greater the list the more time it will take to uncover the unfollowers.
I use who.unfollowed.me and love it.