Unfollow = Manage Flitter

Manage Flitter is an awesome application to unfollow those tweeps who don't follow you back. All you need to do is to connect your twitter account to manage flitter. After loading your statistics,it would categorize people into different groups: not following you back, inactive and people without a display picture. You can go through the desired list and unfollow those people whom you don't want to follow anymore.