There are times when you’d like to have a certain type of post appear in a widget for use in your sidebar or (in some themes) your header or footer.
I used this to display a random senryu on each page, but it will work equally well for any group of reasonably small posts.
There is the option to include the title of the post, the title of the widget, both titles, or neither.
If you want you can add a bunch of widgets, each showing up to five random posts from a different category.

Random One Cat Widget

This Widget shows up to five random posts from a given category

Micah Wood

imzodigital

The Random Post on Refresh plugin allows you to randomly display a different post on every page load.
Using this plugin is simple:
<ol>
<li>Install the plugin</li>
<li>Activate the plugin</li>
<li>On the page or post where you want to have a random post display, add the <code>[random_post_on_refresh]</code> shortcode where you want your post to appear.</li>
<li>Save your changes.</li>
</ol>
<h4>Features</h4>
<ul>
<li>Works with custom post types</li>
<li>No settings page, just an easy way for you to add random posts to your site</li>
<li>Clean, well written code that won’t bog down your site</li>
</ul>

Random One Cat Widget vs Random Post on Refresh