Samer Bechara

This plugin allows your website visitors to set the number of posts they see per page. It will insert a form at the top of your posts page in order to allow your website visitors to quickly set the number of posts they want to see per page.
Detailed Features
User Posts Per Page allows your website visitors to set the number of posts per page, and remembers that number everytime they reach your website.
<ul>
<li>Works with posts, pages and custom post types </li>
<li>Works on Category pages, tag pages, author pages, archive pages, and custom post type archive pages.</li>
<li>Number of posts per page remembered for logged in users</li>
<li>Cookie set for non-logged in users to remember settings</li>
<li>On network installs, network administrator is able to set the default number of posts per page across the whole network</li>
</ul>
Plugin Usage
<ul>
<li>Go to Appearance->Widgets and add your widget to any sidebar of any archive page</li>
<li>Alternatively, you can use the shortcode [user_posts_per_page] to insert this in your theme using 
the function <code>echo do_shortcode('[user_posts_per_page]');</code></li>
</ul>

User Posts Per Page

Allows the user to dynamically set the number of posts to show per page on category pages, tag pages, author pages and all other archive pages.

Wonderflow BV

This plugin is no longer available

User Posts Per Page vs Wonderflow