petermolnar

Parse the_content with <a href="http://www.parsedown.org/demo?extra=1" rel="nofollow ugc">Parsedown Extra</a> to display <a href="https://en.wikipedia.org/wiki/Markdown_Extra" rel="nofollow ugc">Markdown Extra</a> content in HTML parser.

WP-Parsedown

Parse the_content with Parsedown Extra to display Markdown Extra content in HTML parser.

JHoppe

Damn simple [markdown]#via shortcode[/markdown] for wordpress. 
This plugin uses <a href="http://parsedown.org/" rel="nofollow ugc">parsedown</a> and <a href="http://highlightjs.org" rel="nofollow ugc">highlight.js</a>. Zero configuration.
Write this into the editor:
<pre><code>[markdown] 
#h1
</code></pre>
<h3>h2</h3>
<pre><code>text 
____source code (two ore more underscores will be replaced by empty spaces) 
____source code (two ore more underscores will be replaced by empty spaces) 

 `javascript
source code
 `
[/markdown]
</code></pre>
and the shortcode content will be parsed with parsedown. Syntax highlighting will appear for the source codes.
This plugin is available at <a href="https://github.com/JohannesHoppe/markdown-shortcode" rel="nofollow ugc">github</a>, too. 
Please report issues at github, pull requests are welcome, too!

Markdown Shortcode

Damn simple markdown for wordpress via shortcode, uses parsedown (parsedown.org) and highlight.js (highlightjs.org).

WP-Parsedown vs Markdown Shortcode