Josh Betz

Changes the Short URL and the Twitter Tools URL for each post on your site using a custom, shortened domain and a base-36 encode of the post ID.

JB Shortener

Changes the Short URL and the Twitter Tools URL for each post on your site using a custom, shortened domain and a base-36 encode of the post ID.

Prasanna SP

Short Links are easy to remember and share. If you are using WordPress pretty permalinks, your post URLs may be too long to share it on microblogging sites like twitter and identi.ca. This plugin shows Short Link a.k.a ugly default URLs after your post or page content. Short Links will be like http://example.com/?p=123. You can just click on it to select the Short Link. Copy it and you’re ready to share your page on the web! The default title for Short Links is “Short Link:”. You can change it for posts and pages in plugin options page.
Demo: See demo of this plugin here – <a href="http://demo.prasannasp.net/short-link/" rel="nofollow ugc">Short Link WordPress plugin demo</a>
Support: Please post your support questions at <a href="http://forum.prasannasp.net/forum/plugin-support/short-link/" rel="nofollow ugc">Short Link plugin support forum</a>
Visit <a href="http://www.prasannasp.net/wordpress-plugins/" rel="nofollow ugc">this page</a> for more WordPress Plugins from the developer.
<h4>How to style the output?</h4>
The output of this plugin is wrapped in <code></code> tag. Use <code>.short-link</code> CSS class to style it 
Example,
<pre><code>.short-link {
color: #FF0000;
}
</code></pre>

Short Link

Show Short Link for all of your blog posts and optionally for pages with this plugin

JB Shortener vs Short Link