The RT bookmarklet helps you to post a retweet by unofficial style like "RT @kawanet: ..."
[ RT ]
Use the RT bookmarklet on tweet status (detail) page like below:
The tweet content will be quoted in a new tweet:
BONUS
This also runs at any other domain of twitter.com as a shortcut for http://twitter.com/ top.UPDATES
2010.10.09 #NewTwitter interface supported.* Original post of this is written in Japanese.