mmfilesi

This plugin shows in the sidebar n post related with the same category(s) of post being viewed. 
The result can be random or chronological order.
Este plugin es un widget que se incluye en el sidebar. Muestra n entradas relacionas con la entrada que se ha cargado. 
Los resultados pueden ordenarse de forma aleatoria o por orden cronologico.
<h3>Donations</h3>
http://www.mmfilesi.com

mmfilesi-random-post

This plugin shows in the sidebar n post related with the same category(s) of post being viewed.

pantsonhead

RandomText is a handy WordPress plugin that allows you to save, edit and delete categorized text, and inject random/rotated text by category into the sidebar (via widget) or page body (via template tags). The sidebar widget allows you to set an optional Title, and text header and footer. You could say RandomText picks up where the Text widget left off. Whether you want to display random/rotated trivia, quotes, helpful hints, featured articles, or snippets of html, you can do it all easily with RandomText.

Random Text

Store and display random/rotated text by category in sidebar widget or templates.

mmfilesi-random-post vs Random Text