You may know by this time that Twitter has made simple adding Tweet this button on you site. Adding tweet this button on your blog or website is very easy. It is as easy as adding Facebook Like button.
<a class="l-fl" href="http://twitter.com/share?url=http://www.satya-weblog.com<?php echo urlencode($_SERVER['REQUEST_URI']); ?>&text=<?php the_title();?>&via=satya61229&related=webscripting" target="_blank"><img src="http://lh3.ggpht.com/_Ve5n9uU6iBI/TGWNgnlv6II/AAAAAAAABIo/dbXSzhuDARw/s800/twitter.png" width="65px" height="23px"/></a>
Values to change are: 1. Site address (http://www.satya-weblog.com), 2. via (satya61229), 3. related (webscripting). Related is an extra account you can give so that those who tweet your post can be given option to follow both account.
For more options for adding Tweet/reTweet button, head towards Twitter Website.