The app so nice he made it Twice! Tweetie 2 is an award-winning Twitter app for the iPhone and iPod Touch, stowing away an unbelievable number of features into a simple, easy, attractive interface. Seriously!! Every pixel of this interface is precisely designed and intuitive to use.
Echofon for iPhone, formerly TwitterFon, is a super-fast, easy-to-use Twitter app sporting video recording. They changed their name presumably to remove the whole word Twitter out of the app name to avoid trademark trouble. Although the free version is definitely stripped down compared to their $4.99 Pro version, Echofon for iPhone has quite a few features:
Nambu is a feature-rich Twitter app for Mac OS X that supports many social networks. It offers plenty of configuration options but has simple defaults for beginners. It also has excellent integration with its sister services, tr.im and pic.im
Twitterrific for iPhone is a fantastic, feature-packed iPhone twitter app for beginning and advanced users alike. First of all, their 2.0 release saw a major performance and feature overhaul compared to the original version, which was a great twitter app to begin with. This interface is amazing! It's quick and responsive, and scrolling past a hundred tweets with one flick is no problem. But it's not just looks, because there is a LOT packed under the hood: