Friendbar – See your incoming tweets right in the toolbar as well as post updates of your own. Also works with Facebook friends.
Twitter Line – Displays incoming tweets from your friends timeline in a toolbar, and allows you to post updates to your own account.
Twitter StatusBar – A discrete tool that collapses into your status bar when not in use. Just click on the “T” symbol to bring it up and send out your latest update.
Twitter Toolbar – A toolbar that allows you to post updates any time you want as you browse. Also includes pre-written messages for common sayings on the service.
TwitBin – Opens up a Twitter client in your sidebar so you can send and read tweets no matter where you are on the Web without changing tabs or windows.
TwitKit – A sidebar Twitter client that breaks down into tabs for @replies, account stats, public timeline, sending tweets, your friends’ latest tweets and a list of all your followers.
TwitterBar – Type your tweets in the address bar and press the icon at the end to send them. Also allows you to easily tweet about the page you are currently looking at by leaving it in the address bar when you type out your message.
TwitterFox – A Twitter client for Firefox that will allow you to see your friend updates, add your own, retweet, delete read tweets from your stream and more.
BlogRovR – While mainly a tool to help you see linked blog posts as you surf the Web, you can also send out tweets about what you are reading and share them with your followers.
Clipmarks – Clip parts of a Web page that you specifically want to share, and then share them with all of your Twitter followers amongst other services.
DashBlog – DashBlog lets you easily tweet about items you find on the web such as videos, text, quotes, images and more. Also works with Tumblr, WordPress and Blogger.
Feedly – A magazine style feed reader that allows you to tweet about any post you read and find interesting.
Mahalo Share – Share sites you find interesting across multiple services including Twitter.
Power Twitter – Power Twitter adds several features such as revealing the URL behind TinyURLs, embedding of YouTube videos, showing Flickr streams and a whole lot more.
Tw-autocomplete – Allows for autocomplete of Twitter usernames for @ and D messages as you are typing them on the Twitter site.
TweetStalk – Adds a “Stalk” button next to the “Follow” button on Twitter so you can follow someone without them knowing it. Can also create an RSS feed of their tweets so you can read them in your favorite reader.
TwitThat – A bookmarklet that lets you tweet about the current Web page you are reading.
TwitterEyes – An extension to be used specifically on the Twitter site that will keep track of your characters entered and assist you in shortening your message when necessary.
Twitter Search – The name says it all for this handy tool that gives you access to the real-time Twitter search.
TwittyTunes – Works with FoxyTunes to submit the songs you listen to that you wish to share with the Twitter community. If you choose not to use it with FoxyTunes, you can also post about sites and videos you are viewing.
Twitzer – Allows you to tweet messages longer than 140 characters by adding a link to the overflow text, you can also de-Twitzer text and have it displayed directly on the Twitter site
Yoono – Yoono allows you to combine various social networks, instant messengers and other tools into your sidebar, and allows you to send tweets no matter where you are on the World Wide Web at the time.
mais em : mashable