MonkeyFly integrates some really awesome features to twitter’s web interface. Users can create tweetdeck like columns, upload image directly to twitpic etc. MonkeyFly is available as userscript, Firefox add-on and Chrome extension.

The userscript Clean Sidebar removes unwanted elements from the sidebar of twitter homepage.

Twitter Lists are upcoming feature which enable users to create tweep lists.

Vidly is a video sharing site for twitter. It is just like twitpic for videos.

Discover who follows whom on twitter and get common friends and followers. Tool to find more relevant twitter users.

How can you follow those thousands of people on twitter?

Mixero is a powerful twitter client and can be a substitute for Tweetdeck.