Unfollow Twitter Users with iUnfollow
iUnfollow is another twitter tool to bulk unfollow Twitter followers who do not follow you back, you can also add a whitelist and track history.
Use UnTweeps to Unfollow Inactive Twitter Users
Unfollow inactive Twitter users with UnTweeps which lists users who haven't tweeted in a number of days so you can bulk unfollow twitter users.
Bulk Unfollow Twitter Users with ManageTwitter
ManageTwitter is a website which allows you to filter and bulk unfollow twitter users so you can cleanup your following list.
Bulk Unfollow Twitter Users with JustUnfollow
I have been looking for a decent replacement for huitter mutuality and the creator of JustUnfollow had me look at their site. It is useful and simple to use.