isnowfy

My Related Posts Plugin can generate a related posts with thumbnail.

my-related-posts

My Related Posts Plugin can generate a related posts with thumbnail.

piffpaffpuff

Related Links gives you the possibility to manually link other posts to your current post. But you can also link pages, media or any custom post-type. And in addition you can use custom urls to link to external files. The plugin adds a Metabox to the writing page with a list of all available content.
Features:
<ul>
<li>Shows a list of all available content in a Metabox on the writing page</li>
<li>Multiple links can be selected</li>
<li>Link order can be changed through drag and drop</li>
<li>Custom URLs can be added</li>
<li>Search field to quickly find a link</li>
<li>Simple theme integration with an included widget or <code>related_links()</code></li>
<li>Works with custom post-types</li>
<li>Settings to enable the post-types that should be shown in the Metabox</li>
</ul>

my-related-posts vs Related Links