Four Nodes

Simple plugin to display random posts on your wordpress blog. Plugin provides a widget to display random posts in sidebar. 
Also comes with a shortcode [randomposts] to include on pages.
<ul>
<li>Easy to install</li>
<li>Picks Random Posts</li>
<li>Ability to select from specific category</li>
<li>Limit number of posts</li>
<li>Shortcode support</li>
</ul>

FourNodes Random Post

Displays Random wordpress posts in a sidebar widget. Also, provides shortcode to display random posts on pages.

littlejon

LJ Random or Recent is a WordPress plugin/widget that allows you to display a list of Random or Recent posts depending of the type of pages that is being displayed. This plugin can also assist your site for SEO by digging up and making your older content relevant.
The idea was taken from the iNove theme which by default has a similar setup in the sidebar, I just wanted a little bit more functionality plus the ability to put the widget anywhere on the page with any theme.

LJ Random Or Recent

LJ Random or Recent is a Wordpress widget that will display a list of Random or Recent posts depending of the type of pages that is being displayed.

FourNodes Random Post vs LJ Random Or Recent