microkid

This powerful plugin makes it super easy to manually select related posts for your content. You can search and select posts that fit your criteria, all from within the write/edit post screen.
Creating a system of related items on your website will result in more page views per unique visitor, and will improve Google’s understanding of your content.
As mentioned by <a href="http://yoast.com/articles/wordpress-seo/#relatedposts" title="WordPress SEO and Related Posts " rel="nofollow ugc">WordPress SEO</a> master Yoast:
<blockquote>
A very good alternative is Microkid’s related post plugin, which lets you manually pick related posts. This might cost a bit more time before you hit publish but might very well be worth your while.
</blockquote>
You can display related posts automatically underneath your content, use a shortcode or use the widget. Or, if you have some development skills, you can use one of the available API functions for full control of the way related posts are displayed on your website.
With its full support for Custom Post Types, this plugin will work perfectly for both basic and advanced WordPress installations.
See the official plugin homepage for <a href="http://www.microkid.net/wordpress/related-posts/" title="Wordpress Related Posts" rel="nofollow ugc">Related Posts for WordPress</a> for more info and discussion.
<h4>Features</h4>
<ul>
<li>Easily find posts or pages that might be related to the one you are writing with an integrated AJAX powered search utility</li>
<li>Easily add and remove relations with a single click</li>
<li>Extreme flexibility in the customization of the way the related posts are displayed on your website</li>
<li>The relationship created works reciprocal, which means that if post A is added as related to post B, post B is automatically added as related to post A as well (this option can be turned off easily through the settings panel)</li>
<li>Custom post types support</li>
<li>Multiple widget support with extended customization options</li>
<li>Shortcode support: add the [related-posts] shortcode to your post content to display related posts anywhere you want</li>
<li>Automatically display a list of related posts underneath your posts content. No need to add any PHP tags in your template files, but several <a href="http://www.microkid.net/wordpress/related-posts/#API" title="Related Posts for WordPress API functions" rel="nofollow ugc">functions</a> available for advanced users.</li>
<li>Available in a growing number of languages</li>
</ul>

So far good

Increase your pageviews and SEO by manually selecting related posts for your content. Easy reciprocal linking of related posts and pages.

Dimox

Displays the structured list of categories (like in article directory), which can be easily customized with CSS. Also allows authors to publish articles and change their profile bypassing the admin interface. See the demo at <a href="http://articlesss.com/demo/" title="Article Directory" rel="nofollow ugc">Articlesss.com/demo/</a>.
Standard features for categories list:
<ul>
<li>Showing an amount of articles in parent and child categories.</li>
<li>Showing a category description in link title.</li>
<li>Showing the empty categories.</li>
<li>Using hierarchy for subcategories.</li>
<li>Excluding a specified categories.</li>
</ul>
Special features for categories list:
<ul>
<li>Simple and handy design using CSS. The structure of categories is the multilevel list, which can be altered easily with CSS, as you need. The parent category have the <code><div></code> container to mark it out with CSS as a parent.</li>
<li>Parent category is showing amount of articles in subcategories. The character also include the number of articles in this parent category.</li>
<li>Showing a specified amount of child categories (2nd level).</li>
<li>Showing a categories in specified amount of columns.</li>
<li>Hiding all subcategories.</li>
<li>Adding an icons for each category in the list using CSS.</li>
</ul>
Additional features:
<ul>
<li>Authors can add articles and change their profile bypassing the admin interface.</li>
<li>Displaying the “Terms of article publication” on article submission page.</li>
<li>Excluding the child categories articles from the parent categories archive pages.</li>
<li>Ability to get an article source code.</li>
</ul>

Article Directory

Displays the list of categories like in article directory and allows authors to publish articles and change their profile bypassing the admin area.

Related Posts for WordPress vs Article Directory