Gwibber - Gwibber is an open source microblogging client for GNOME developed with Python and GTK.
YoruFukurou - YoruFukurou (NightOwl) is a Twitter client for Mac OS X, designed for Twitter addicts.
TweetDeck - TweetDeck is your personal browser for staying in touch with what’s happening now.
Janetter - Janetter is a Twitter client application. Faster, smarter, and more powerful.
Tweetbot - Sync your timeline across your iPhone, iPad, and Mac. Mute tweets by user, hashtag, tweet source, or keywords (including regex). 3rd Party support for image, video, read later, and timeline sync services.
Talon for Twitter - Elegantly designed, ad-free Twitter experience for Android