Twitter - Managing Your Account

Hummingbird - Very robust & professional tool for organization. One of the best out there. For serious Twitter Users.

TweetDeck - Free application you download to your desktop. Lot of Twitter users use this. Pretty easy to use.

Twitterrific - Let's you both read & publish posts directly to Twitter. Multiple account support. Clean & easy to use.

Mad Twitter - A Windows application that lets you read & post Tweets.

Twitter-r - A Twitter File sharing application.

Twoogle - Search Twitter & Google at the same time.

Twidget - A program you install on your desktop that auto-refreshes Twitter. Watch Twitter, without logging into Twitter.com

Twhirl - A desktop client for social media softwares such as Twitter, Friendfeed, identica. & seesmic.

Twinja - Desktop twitter application

Snitter - Yest another Twitter Desktop Application.

Splitweet - Manage multiple applications & your online brand.

Power Twitter - Excellent Firefox add on