Automattic

John Godley

Donncha O Caoimh (a11n)

Eoin Gallagher

Lenny

Future upgrades to Sharedaddy plugin will only be available in <a href="http://jetpack.me/" rel="nofollow ugc">Jetpack</a>.
Jetpack connects your blog to the WordPress.com cloud, <a href="http://jetpack.me/support/" rel="nofollow ugc">enabling awesome features</a>.

Sharedaddy

Future upgrades to Sharedaddy plugin will only be available in Jetpack.

Ruven

This plugin provides a function to output links to share a post to Facebook, Twitter, and Google+.
Selected themes by Ruven will display the links automatically when the plugin is activated. 
In other themes you will have to edit the templates in your theme in order to output the links.
Here an example of outputting the links in as list:
<pre><code><?php
if(function_exists('ruven_sharing_links')) {
 echo '<ul class="sharing-list">';
 $sharing_links = ruven_sharing_links();
 foreach($sharing_links as $sharing_link) {
 echo "<li>$sharing_link</li>";
 }
 echo '</ul>';
}
?>
</code></pre>
<h4>Usage</h4>
<pre><code>$sharing_links = ruven_sharing_links( $get_array, $include, $open_in_new_tab, $class );
</code></pre>
<h4>Parameters</h4>
$get_array 
(bool) (optional) If you want the return value to be an associative array (title, URL) or an array of HTML links. By getting an associative array, you are able to customize the output more.
Default: false
$include 
(array) (optional) If you don’t want all platforms (Facebook, Twitter, and Google+) included, you can specify here which you want specifically to be returned. E.g. <code>array('Twitter', 'Facebook')</code> would only return Twitter and Facebook links.
Default: array()
$open_in_new_tab 
(bool) (optional) If you want the sharing dialog to be opened in a new tab/window or not.
Default: true
$class 
(array) (optional) Classes you want to add to the links. E.g. <code>array('sharing-button', 'big-button')</code>
Default: array()
<h4>Return Value</h4>
If the value of <code>$get_array</code> is <code>false</code> (default), the function returns an array of HTML links.
If the value of <code>$get_array</code> is <code>true</code>, the function returns an associative array of the title (e.g. “Twitter”) and the URL to share the post.

Ruven Themes: Sharing Links

RT Sharing Links provides a function to output links to share a post to Facebook, Twitter, and Google+.

Sharedaddy vs Ruven Themes: Sharing Links