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.

mapteo

If readers of your wordpress site/blog come across a snippet of text they want to Tweet, you know the drill: they have to copy it, open Twitter, create a new message, then paste in the text there and then hit the send button…it’s not that difficult, but what if there was an even easier way? 
Well, there is, and here it is. TweetEverything allows tweeting highlighted text with a single click. See screenshots.
<h3>Developer Documentation:</h3>
Want to contribute? Visit <a href="https://github.com/mapteo/TweetEverything" title="TweetEverything on GitHub" rel="nofollow ugc">TweetEverything on GitHub</a>.

TweetEverything

TweetEverything allows tweeting highlighted text.

WP-TweetButton Plus vs TweetEverything