ruudkok

With this plugin you can add the new Tweet button from Twitter to every post, and every page. The plugin is fully customizable:
<ul>
<li>Choose where to display the button (top,bottom,left,right), up to 2 times each post/page</li>
<li>Choose when to display the button (posts, pages, both or everywhere)</li>
<li>Select the type of button you like (horizontal count, vertical count, or no count)</li>
<li>Set the margins between the Twitter Button and surrounding content</li>
<li>Select a twitter account (if any) which you want to be mentioned in each tweet (e.g. via @ruudkok)</li>
</ul>

WP Twitter Button

This plugin allows you to add the new Twitter button(s) to your blog. You can choose the type of button and set where to display the buttons.

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.

WP Twitter Button vs WP-TweetButton Plus