Twellow is a new Twitter Directory which has been launched by the folks at iEntry/WebProNews and looks like it will be quite a piece of work. Taking elements from Twitter, web directories, search engines and the Yellow Pages, Twellow.com lets Twitter users add their Twitter profile to the vertically categorized directory; along with basic personal info, their web site and amount of followers (all taken from a Twitter account, I'd like to see the option to login, verify the account, and add more info).
Twitter users are then ranked under each category by the amount of followers, and their Twellow profiles are updated when the users update Twitter. Furthermore, each Twellow user gets their own personal profile page, (with a natural link to their site I may add).