John

This plugin enables you to highlight syntax using the PEAR Text_Highlighter class. Other syntax highlighters that use GeSHi have slower rendering speeds which will increase your page load time. However, this plugin gives you the speed and efficiency provided by the PEAR developers. You even have the option of enabling or disabling the line numbers as well as specifying your own style.

Ion Snytax Highlighter

This plugin allows users to highlight code.

Rachel Baker

This plugin uses the <a href="http://projects.serenity.de/textmate/" rel="nofollow ugc">Sunburst theme</a>, a colorful and high contrast dark theme to highlight your code syntax with <a href="http://softwaremaniacs.org/soft/highlight/en/" rel="nofollow ugc">Highlight.js</a>. Highlight.js is accurate, fast, lightweight and easy to use.
Usage
Short-code method:
<ol>
<li>From within a WordPress page or post, wrap the <code>[prettify][/prettify]</code> shortcode around the code snippet you wish to highlight.</li>
<li>You can specify a language by specifying the language extension inside the shortcode. 
Example: 
[prettify class=”html”][/prettify]</li>
<li>The shortcode will work from within either the Visual or HTML editor.</li>
</ol>
Non-short-code method:
<ol>
<li>
Wrap your code snippets in “
.
</li>
<li>You can specify a language by specifying a class in the <code>element. 
Example: 
<pre><code class="html"></code></li>
</ol>
Sunburst Only
This plugin only contains the CSS file for the Sunburst theme syntax highlighting formatting, because it is the best dark syntax theme. If (for some reason) you wanted to highlight your code using a different theme, there are other syntax highlighting themes available in the <a href="http://softwaremaniacs.org/media/soft/highlight/test.html" rel="nofollow ugc">Highlight.js Theme Gallery</a>
Languages Supported:
<ul>
<li>Bash</li>
<li>C#</li>
<li>C++</li>
<li>CSS</li>
<li>Diff</li>
<li>HTML, XML</li>
<li>Ini</li>
<li>Java</li>
<li>JavaScript</li>
<li>PHP</li>
<li>Perl</li>
<li>Python</li>
<li>Ruby</li>
<li>SQL</li>
</ul>

Sunburst Code Prettify

Uses Highlight.js with the Sunburst syntax theme to elegantly highlight code.

Ion Snytax Highlighter vs Sunburst Code Prettify