Kodetop

This plugin allow insert Tweet Button on your blog or site. The button can be customized in the settings page. Tweet Button can be positioned a the top, bottom of content. You can use text shortcut <code></code> and PHP function <code>wp_tweetbutton();</code> for manual insert.
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 Related Account</li>
<li>Config Tweet text</li>
<li>Config display locations (entries, pages, home page)</li>
<li>Config position in content (before, after, none)</li>
<li>Text shorcut: <code></code></li>
<li>PHP Function: <code>wp_tweetbutton();</code></li>
</ul>
Manual usage of WP-TweetButton:
For include into post content use: <code></code>
For include in your template use: <code><?php wp_twitterbutton(); ?></code>
For more information visit <a href="http://blog.unijimpe.net/wp-tweetbutton/" title="plugin website" rel="nofollow ugc">plugin website</a>

WP-TweetButton Plus

This plugin allow insert Tweet Button on your blog or site.

ChefGaby

This plugin will help you add the official twitter button in your articles. It’s easy to customize and works right after activation. 
You will be able to choose where the button shows up inside an article, what type of twitter button to show and what text to submit when a user clicks the button.

Easy Twitter Button

Add the official twitter button in your articles

WP-TweetButton Plus vs Easy Twitter Button