UPDATE: As of June 1, 2011, this method is no longer supported by Twitter. Thanks to Asif Khan for posting in the comments. I recommend you use Twitter’s official Tweet Button instead. Details on using the Twitter share link to come.
I saw this nice technique the other day that enables someone just click a link to Tweet a message about you that pre-fills the message. It’s a hyperlink that opens up Twitter.com and auto-fills the status message box with a message of your choosing. It works whether or not the person is already logged into Twitter.
The format is
<a href=”http://twitter.com/home?status=Put your message here and include your username ala @johnmccrory”>Tweet this</a>
or in just URL form
http://twitter.com/home?status=Put your message here and include your username ala @johnmcccrory
If you use %20 in place of spaces in that message part of that URL (the words after status=), you can shorten it with most URL shorteners and put it in a tweet, too:
All the person needs to do is click your link and then hit the update button in Twitter. Couldn’t be simpler!
UPDATE 11/23/2009: Tweetmeme offers a Retweet button plugin for WordPress that does this in an elegant manner for WordPress blogs.