dev.Fishy

EN:
Adds a simple widget to the sidebar that displays a random posts.
RU:
Добавляет простой виджет в боковую панель сайта, который отображает случайные посты.

RandPost widget

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.

RandPost widget vs FourNodes Random Post