Allan Collins

This plugin will allow you to add code snippets to your pages/posts. This is great for code tutorial sites.
<h3>Upgrading</h3>
If you are upgrading from version 1.0, you will see an option on the Code Library page that will allow you to upgrade. As a precautionary measure, be sure to back up your database before doing so.

WordPress Code Snippet

This plugin will allow you to add code snippets to your pages/posts.  This is great for code tutorial sites.

Arul

Smartpixels

<a href="http://www.smartpixels.net/?post_type=products&p=190" rel="nofollow ugc">Smart Syntax</a> plugin automatically adds Google prettify syntax highlighting to the fenced code blocks in both content and comments.
It’s made with <a href="http://jetpack.me/" rel="nofollow ugc">Jetpack</a> markdown in mind, which brings the power of markdown extra to WordPress and gives you an easy to use markdown syntax for fenced code blocks.
For more information on usage and features, check out <a href="http://www.smartpixels.net/?post_type=products&p=190" rel="nofollow ugc">smartpixels</a>.

Smart Syntax

Automatic google prettify syntax highlighting for jetpack markdown fenced code blocks

WordPress Code Snippet vs Smart Syntax