James Kemp

This plugin allows you to list any number of related posts from the same category as the current post. You can also randomise these results. It is very lightweight, at only 3KB.
There are a number of options available:
<ul>
<li>Choose the number of Posts to show</li>
<li>Choose whether it displays these posts randomly, or in order specified by you.</li>
<li>Choose whether to display a title, what tags to use, and what text should be displayed (e.g. H3)</li>
<li>Choose a class for the main UL</li>
</ul>
To display the random related posts in its simplest form, simply place the following code in your single.php file – <code><?php relatedPosts(); ?></code>.
To edit the options availble, use the following codes:
<pre><code><?php relatedPosts(
 $ppp = 4, 
 $rand = true, 
 $rPinctitle = true, 
 $rPtitletag = 'h3', 
 $rPtitle = 'Related Posts', 
 $rPulclass = 'related_posts',
 $orderby = 'title', 
 $order = 'ASC'
); ?>
</code></pre>
Where:
<ul>
<li>$ppp = Number of posts to display (Any integer allowed)</li>
<li>$rand = sets the display to random (true/false)</li>
<li>$rPinctitle = Displays the title (true/false)</li>
<li>$rPtitletag = The type of tag to wrap the title in (Default h3, but it can be any valid HTML tag)</li>
<li>$rPtitle = The title to be displayed (This can be any text value)</li>
<li>$rPulclass = This sets the class of the ul (This can be any text value)</li>
<li>$rPexcerpt = Displays the post excerpt (true/false)</li>
<li>$orderby = This allows you to order the posts by certain parameters (title/author/date/modified/menu_order/parent/ID/none/comment_count) If you want to choose the order of your posts, be sure to set $rand to false</li>
<li>$order = This can either be Ascending or Descending (ASC/DESC)</li>
</ul>

Random Related Posts Based on Category

This plugin allows you to list any number of related posts from the same category as the current post. You can also randomise these results.

shisuh

This is a good-design and responsive related page plugin. 
If you do not want fix design by yourself or you want to increase PV , this plugin is for you.
Features
1.Inspite of you set different aspect ratio thumbnails , posts line-up exactly horizontal as yahoo-tech.
better design for:Gadget,Gourmet,Viral Media
2.Infinity scroll increase count of impression as twitter or facebook
increase pv for:website has many posts
3.Good designed for Smartphone / Tablet / PC
increase ov for:website has pc , tablet , smartphone users
Technical Features
This plugin do not delay load , because javascript load posts from our server after load post.
(Japanese Below)
関連ページをいい感じの見た目でレコメンドするツールです。
関連ページのデザイン崩れを放置している方、閲覧数を増やしたいメディアやブロガー様にお使い頂いております。
３つの特徴と用途
・タテ・ヨコ比が違ってもきれいに並ぶ
見た目が向上するサイト：ガジェット・グルメ・バイラルメディア
・スクロールで多くの記事を推薦できる
PV増が期待出来るサイト：テキスト中心、画像中心、記事数が多い
・スマホ / PC / タブレットあらゆるサイズのデバイス対応
PV増が期待出来るサイト：制作系、検索に強い、PCでもアクセスされやすい

Random Related Posts Based on Category vs Related Posts Line-up-Exactly by Milliard