Tweepi is a free tool for finding the most interactive tweeps to follow and unfollowing the deadbeats using Tweepi's [geeky] Twitter scripts.
Why geeky? Well, Tweepi uniquely provides numbers in a customizable/sortable table for you to pick the tweeps that best match you interests. For example, people who are active, reply much, retweet and get retweeted a lot and so on.
Very nice. This is the best non-blackhat tool to manage followers, but since it works via OAuth, only one account at a time. UI is good enough, loads fairly quick, and offers features I haven't seen before like:
The ability to add/remove columns with sorting is fantastic. Create and edit list quickly.
The included smart preset filters like reach/influence, klout, linkers (probably spam followers), talkers (rarely follow back or engage.
When the paid version comes out it could become a worth investment.
When I want to "flush" people who aren't following me back, this is the ultimate app. I don't flush everyone. There's people I find interesting and follow regardless. However, sometimes people follow me to get me to follow back and then unfollow --- flush! It also has tons of stats to analyze your followers to see whose "real" and engaged vs the spammers and the like.