WhizKins

WPSimpleInsert is a plugin to insert custom code in your blog posts. It includes options to either add the code above 
or below post content.
Features:
<ul>
<li>Add custom HTML/PHP/JavaScript to your posts.</li>
<li>Ability to add custom code above or below post content.</li>
<li>Options to hide the code from certain pages like the home page and category and archives pages.</li>
</ul>

WP Simple Insert

A plugin to insert custom HTML or PHP code in your posts. Includes options to insert before or after post content.

Gaiaz Iusipov

Simplest plugin that allow to inject any code into footer of a web page.

Footer Code

Simplest plugin that injects any code into footer of a web page.

WP Simple Insert vs Footer Code