Twitterless – Tells you who stops following you and graphs your follower history over time, making this info available in a variety of useful views.

appTracks: Web
appTags: followers, following, graphs, lost followers

Twitter Karma – See and compare who you follow, who follows you, and reciprocal follows.

appTracks: Web
appTags: followers, following

FriendorFollow – Find out who’s not following you back and who’s following you that you’re not following.

appTracks: Web
appTags: followers, following, process followers, tracking