Ady Romantika

This simple plugin is a widget that displays a list of random posts on your widgetized sidebar.
It supports multiple instances with WordPress 2.8 and above.
<h3>Configuration</h3>
<ul>
<li>Widget title: the title of the widget</li>
<li>List types: ul for bulleted list, p for paragraph, br for paragraph with line breaks</li>
<li>Post count: Number of random posts you would like to be displayed</li>
<li>Category: Only this category will be selected as the source</li>
</ul>

Random Posts Widget

This simple plugin is a widget that displays a list of random posts on your widgetized sidebar. It supports multiple instances with WordPress 2.

ray.viljoen

Fubra

The plugin provides a sidebar widget with customisable title and number of related posts to display. 
The widget will display a random list of x number of posts ( selected in widget options ) together with a small tag including the publish date and author. 
If used outside of a specific category the widget will default to all categories, whilst still displaying the selected number of random posts.
Developed by <a href="http://www.catn.com" rel="nofollow ugc">PHP Hosting Experts CatN</a>

Random Related Posts

A simple sidebar widget to include a custom number of posts from the same category as the current post.

Random Posts Widget vs Random Related Posts