FlashTweet
FlashTweet is a Twitter application that simplifies the process of acquiring more targeted followers. You can add multiple Twitter accounts to your profile, discover who you are following that is following you back, mass follow users based on search terms and location, unfollow multiple friends at once, schedule tweets in advance to run throughout the week, insert RSS feeds that will automatically tweet the title and link of your blog or another site.

FriendorFollow
Besides displaying lists of your twiter friends, followers and people you follow you can get most followed user list, user growth chart and other information.

Twitter Karma
Twitter Karma is one of the best sites to unfollow those who do not follow you back on twitter. You can also follow those who follow you but aren’t being followed by you.

Tweetelity
Tweetelity is a simple twitter application that lets you mass unfollow all twitter users who do not follow you back on twitter.

Tweepi
Tweepi is a simple collection of Twitter tools; each tool is designed to make a certain aspect of your Twitter experience and interactions simpler and more enjoyable!

Twitin
TwitIn is a twitter app for following and unfollowing twitter users in bulk.The site also displays your rating based on certain criteria. You can bulk unfollow 50 twitter users at a time and follow upto 25 at one go.