I've been going through several different Twitter applications that run on Mac, from Nambu to Twitteriffic and now Tweetie, all had their pros/cons but it turns out Tweetie is the best for me in terms of functionality and visuals.
I also added the Adium icon prior to actually getting Tweetie so I thought that in my dock there's 3 chat clients, Tweetie, Adium and Skype, since 2 of them look the same why not 3? So now I made my own Skype icon to match the others. I may edit the arrow tab on the icon so it's in the middle but that can be another day.
Download: Click Me (Mac OS X) or click here PC users