iFollowBack - Fast Twitter Networking: It is a way to identify, get followed and follow back your friends on Twitter. You sign up and agree to follow back other users. Other users sign up, and agree to follow you.

Twitowl [ remove highlighting ] - Get on the beta list now! The Ultimate set of Twitter Tools. Schedule tweets, Track keywords on Twitter, Save and reuse drafts, Send welcome Direct Messages, Shorten urls and get click stats, Follow those who follow you, Unfollow those who unfollow you, View @Mentions & Retweets, for an unlimited set of Twitter accounts. Many new features on the way! Click here to get notified when TwitOwl launches.

TweepleRank - Ranks the top recommended people on twitter. It does so by monitoring the tags #followfriday, #mrtweet and #tweepletuesday. The site also allows you to search, filter by tag, or even personalize the results to find new and interesting people to follow.

TwitR User Directory where you can track people by tags, and also you can track their followers on a handy graph.

Tweetsmap allows you to see where your followers are from , based on Google Map with built-in database

Twidiots - Find out people, who have left twitter, who do mass-flollow, who has a lot of friends(and probably dont read anybody's updates), who follow some persons, unpleasant for you or those, who simple don't follow you back. All this in 2 clicks. Make your friend list and timeline cleanr!

Twibes - Hand picked friend recommendations

FlashTweet - A mass follow tool that simplifies the process of adding your twitter friends. You can see who you are following that is following you back, follow friends from other users and even unfollow multiple friends at once.