H. Peter Pfeufer

Twitter has provided a twitter and retweet button. This Plugin adds the official twitter button to your blog articles, pages, archives, categories and rss.
Features
<ul>
<li>Easy install</li>
<li>Panel for easy configuration</li>
<li>Config Button Style</li>
<li>Config Language of Button</li>
<li>Config Your Twitter Account</li>
<li>Config Tweet text</li>
<li>Config display locations (entries, pages, home page, archive, category)</li>
<li>Config position in content (before, after, both, manual choice)</li>
</ul>
Note
If you choose the position as “manual choice” you have to edit your template-file and add the following code at a position of your choice. 
 <?php if(function_exists(‘wp_twitterbutton’)) { wp_twitterbutton(); } ?>
Translations
<ul>
<li>English</li>
<li>German</li>
<li>French (by: <a href="http://www.frankoli.de/blog/" rel="nofollow ugc">Frank</a>)</li>
<li>Dutch (by: <a href="http://wpwebshop.com/" rel="nofollow ugc">Rene</a>)</li>
<li>Czech (by: <a href="http://blog.michalbernat.cz/" rel="nofollow ugc">Michal Bernat</a>)</li>
<li>Hebrew (by: <a href="http://www.sagive.co.il/" rel="nofollow ugc">Sagive</a>)</li>
<li>Hindi (by: <a href="http://outshinesolutions.com/" rel="nofollow ugc">Love Chandel</a>)</li>
</ul>

WP-Twitter Retweet Button

This plugin will install the official Twitter Button provided by Twitter to your Wordpress-Blog.

Konstantin Kovshenin

Retweet Anywhere for WordPress is a nice and easy way to allow your readers to instantly retweet your blog posts through their Twitter accounts. It uses the slick Twitter @Anywhere bundle which works through OAuth and never requires your readers to input their Twitter names or passwords.
The plugin is customizable, URLs could be shortened through bit.ly, the retweet format is defined by the blog administrator. Visitors can modify the tweet text before actually sending it to Twitter, allowing them to add hashtags or addressing somebody in particular.
<ul>
<li>Easy to install</li>
<li>Customizable message format</li>
<li>Shortcodes or manual PHP integration</li>
<li>Bit.ly shortened links</li>
<li>Customize Facebox, fading background, etc, super fancy!</li>
<li>Works fine when javascript is disabled</li>
<li>Includes an awesome customizable retweet widget!</li>
<li>Implement the RT button in your text widgets</li>
<li>Supports <a href="https://wordpress.org/extend/plugins/googl/" title="Goo.gl URL Shortening" rel="ugc">Goo.gl URL Shortening</a></li>
<li>On-going development</li>
<li>Literally anywhere!</li>
</ul>
YES, I do consider feature requests, and that is what makes this plugin work. The discussions go here: <a href="http://kovshenin.com/wordpress/plugins/retweet-anywhere/" title="Retweet Anywhere" rel="nofollow ugc">Retweet Anywhere</a>

Retweet Anywhere

Retweet Anywhere for WordPress is a nice and easy way to allow your readers to instantly retweet your blog posts through their Twitter accounts.

WP-Twitter Retweet Button vs Retweet Anywhere