Are you addicted to twitter yet? if yes you must be having atleast one of these, try them out all have their own significance and interface.

Twhirl - Twhirl is probably the most popular desktop client. It also supports TwitPic, TweetScan, FriendFeed and cross posting to Pownce and Jaiku.

Spaz - Desktop client for Mac, Windows and Linux

TweetDeck - Better organize your Twitter friends with a great built in group feature. TweetDeck uses the popular Twitter search engine Summize to do the heavy search lifting. Summize is the premiere search engine for Twitter and was recently purchased by Twitter for that very reason

Tweetr - This one will allows you to send files to other Tweeters. It also has a built in webcam feature.

Alert Thingy - Keeps you updated on FriendFeed and Twitter. Allows you to easy upload pictures to Flickr.

Twitteroo - Displays updates without pictures (for better or worse).

Witty - Open source client for Vista and XP

bTT - Non-Adobe AIR based desktop client.

Twitterlicious - Very minimalist desktop client and extremely easy.

Snitter - Amazing customizable desktop client for Mac and Windows.

Feedalizr - You can use this single client to post to FriendFeed, Twitter, Jaiku and Flickr with this desktop client.

Posty - This one has a support for several microblogging services

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