Riyaz

WP Tweetbox adds a manual tweetbox with Twitter-style editor at the end of posts and pages.
Features:
<ul>
<li>Tweets branded to your website</li>
<li>Fully Customizable Tweetbox</li>
<li>Tweet text can be auto-generated</li>
<li>You can specify a custom Tweet text for individual posts/pages</li>
<li>Tweetbox can be disabled on individual posts/pages</li>
<li>Supports Su.pr, Bit.ly, Bitly.pro, Wp.me URL shorteners</li>
<li>You can use a WordPress short URL with post ID or long permalink URL as well</li>
</ul>

WP Tweetbox

WP Tweetbox adds a highly customizable Tweetbox at the end of blog posts and pages. Tweets are branded with your own website URL.

Binesh Dobhal

go social plugin displays the social media sharing / bookmarking icons for your blog posts . It has buttons for Facebook , Digg, Google Buzz, Twitter & more to be added soon, It also displays number of likes and shares for twitter and facebook in a very neat and clean compact web 2.0 way .

go Social

Enables you to display the social media icons using direct twitter/facebook/buzz/digg  api for every post

WP Tweetbox vs go Social