Manoj

This plugin allows you to choose different template for individual post, for the purpose of single post view, by selecting previously created post template from the provided drop-down list in the post edit screen.
The plugin will replace the default template (single.php) with selected template for the post you applied the new template.
To create a post template, write an opening PHP comment at the top of the file that states the template’s name.
<pre><code><?php
/*
Post Template - Name: Template Name
*/
?>
</code></pre>
Please Note: Post template name ussage: “Post Template – Name:”.

AMS Single Post Template Selector

This plugin allows you to choose different template for individual post.

CyberCraft

Mithu A Quayium

The plugin is to let you choose template for any post of any type as you can choose for page. Thus, every single post of any post type can be loaded/rendered in custom template as you want. 
You have to create template just like those you create for page. These template then will appear in dropdown box in admin panel of post where you select one for the post from.
<h3>Features</h3>
<ul>
<li>
You can select template for any post of any post type !
</li>
<li>
Templates can be create exactly like the page templates, no exceptional coding needed !
</li>
</ul>

WP Post Type Template

The plugin is to let users choose template for any post of any type as you can choose for page.

AMS Single Post Template Selector vs WP Post Type Template