crimson090

Adds buttons to the Text (HTML) edit which generate Markdown syntax. These buttons serve as a great introduction to 
users who are new to Markdown, as well as shortcuts for more experienced users. The buttons include:
<ul>
<li>Bold</li>
<li>Italic</li>
<li>Blockquote</li>
<li>Link</li>
<li>Code</li>
<li>Table</li>
<li>Headers</li>
<li>Help (links to external Github Markdown guide)</li>
</ul>
This plugin does not modify the Visual editor, as that editor is not ideal for writing Markdown in. It’s recommended you disable 
the Visual editor entirely to enforce using Markdown.
Note that this plugin does not render Markdown. You should use a plugin (such as Jetpack Markdown) to render markdown in your theme.

MarkdownBar

Adds a toolbar of buttons to the Text (HTML) edit which generate Markdown syntax

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).

MarkdownBar vs Markdown Shortcode