Directories   

• TweetFind.com -New! Twitter Directory with Twitter Lists  - Search Twitter Lists, Celebrities, Businesses, Users, & Celebrities - Get More Twitter Followers @TweetFind
• FollowFriday.com - New! Twitter ranking of the most recommended tweeps based on the #followfriday recommendations. Check who recommends you and who you have recommended. @followfridaycom
• Resonancers.com - New! See which users get their tweets on Twitter’s home page the most. The best way to find the most influential people on Twitter  whether famous or not. @resonancers
• Socialized Card : Which all social network sites a twitter user have account. Also, let your viewers connect with you on all social network site's you belongs to using your twitter profile url. Socialized Card holds your entire social identity.
• GeoFollow - Local Twitter Search - Geo (location based) twitter directory. (Add youself on twitter by sending @geofollow YOUR CITY, YOUR STATE YOUR ZIP #tag1 #tag2 #tag3. EG: @geofollow Walnut Creek, CA 94596 #directory #geek #people. Largest location based Twitter Directory on the net.
• twitboy - all men on twitter
• twitgirl - all women on twitter
• Twitter-Athletes - A directory of verified professional athletes on Twitter. (NFL, NBA, MLB, NHL, Soccer, Golf, Tennis, MMA, etc)
• Politwitter - Canadian political twitter, list of Canadian MP's and MLA's tweeting.
• Followformation - Quickly follow dozens of categorized Twitter users.
• LocaFollow - A Tool For Searching and Following Other Twitterers - A Twitter search engine that enables you to locate and follow Twitter users by searching in their Bio and Location fields.
• Twibes Twitter Groups - Twitter affinity groups. Find people with similar interests.
• Tweeple411 ~ World's first Tweeple driven Directory. Find people with similar interests to follow or add your Twitter or FriendFeed page. Power to the Tweeple!
• Twitter Directory 2000 - Twitter users that have a minimum of 2,000 followers and have updated status within the last 30 days. Also offers follow and be followed status.
• Twitwho - Human-edited directory of Twitter users organized by categories.
• Zellr - Directory for twitter users. Members can link their twitter profiles with facebook, twitpic, rss, digg and other accounts in a single profile.
• Twapps.com - A twitter gallery that show cases all twitter applications. Growing daily.
• Twitter News - Latest news about twitter at one place
• Twi5 - A one stop shop for finding cool twitter applications.
• Twtapps - We develop simple, fun and useful twitter apps. Our apps don't require username/password!
• App list - A monster list of all web based twitter applications: http://i-stuff.blogspot.com/search/label/Twitter
• TwtBiz -  is business directory for Twitter. You can find businesses, entrepreneurs, investors! See the company's team Twitter feed. (by @twtapps)
• ComedyTweet The daily lives of the funniest comedians on twitter -- all in one place! (follow us at @comedytweet)
• PornStar Tweet! The daily lives of the hottest Porn Stars on twitter -- all in one place! (follow us @pornstartweet)
• ALTGirlTweet! The daily lives of the hottest ALT Models on twitter -- all in one place!  (follow us at @altgirltweet)
• WebGirlTweet! The daily lives of the hottest Web Girls and Cam Girls on twitter -- all in one place! (follow us at @webgirltweet)
• GlamTweet! The daily lives of the hottest Glamour Models on twitter -- all in one place! (follow us at @glamtweet)
• BBWGirlTweet! The daily lives of the hottest BBW Girls on twitter -- all in one place! (follow us at @bbwgirltweet)
• GayStarTweet! The daily lives of the hottest Gay Porn Stars on twitter -- all in one place! (follow us at @gaystartweet)
• PornExec Tweet! The daily lives of the hottest Porn Executives on twitter -- all in one place! (follow us @pornexectweet)
• The Social Archive Topical Directory of Tweets with Downloadable Archives.
• TwitterStates Twitter Directory for United States. (follow @TwitStates)
• RetweetFollow - New! RetweetFollow lets you search by keywords in URLs tweeted and to easily follow the retweeters. You can also create lists, export the results, thank the RTs. 
• Hash Dump  Registration of Twitter hashtags.