Scott Taylor

Like Buttons makes your site instantly share-able. The plugin adds <code><meta></code> tags to your pages’ HTML <code><head></code> which will pull the proper content from your site when someone shares one of your site’s URLs on Facebook. Using some simple Theme functions, you can add Like buttons to posts / pages / custom post types AND a Like button for your blog / website
<pre><code>// in the Loop - for posts / pages / custom post types
the_like_button()

// a Like button for your blog / website, put it anywhere!
the_blog_like_button()

// use this if you don't want to register your app
the_like_iframe()
</code></pre>
Read More: http://scottctaylor.wordpress.com/2011/01/04/new-plugin-like-buttons/

Like Buttons

Adds Open Graph  tags to your posts/pages/etc, adds a Facebook Like button to posts using simple Theme functions. Requires a Facebook Application ID ( …

d-media

Automatically add InShare buttons to your posts. It works for single pages and loops. 
The plugin features an options page in which the following can be configured:
Display options:
<ul>
<li>Toggle hiding of button in loops </li>
</ul>
Display style:
<ul>
<li>Show button on top or bottom of post</li>
<li>Choose button display style (counter top,counter right,default)</li>
<li>Add breaks before and/or after the button</li>
<li>Button preview</li>
<li>Custom styling option, adds a containing div with classname which you can style in your stylesheet (new since 1.1)</li>
</ul>
<h3>Arbitrary section</h3>

LinkedIn InShare button

Automatically add InShare buttons to your posts. It works for single pages and loops and is display options are customizable.

Like Buttons vs LinkedIn InShare button