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

seothemes

Markdown Editor replaces the default WordPress editor with a Markdown editor for your posts and pages. This plugin uses the Jetpack Markdown module for converting Markdown into HTML and plays nicely with Jetpack if both plugins are installed.
There are 4 editor layouts to choose from when writing posts: default, preview, full-screen and split screen. Changes are updated automatically allowing you to preview your content as you write.
By default Markdown Editor is only enabled on Posts, but you can enable it on pages and custom post types by adding post type support. For example to add Markdown support to Pages, add the following line of code to your theme’s functions.php file:
<pre><code>add_post_type_support( 'page', 'wpcom-markdown' );
</code></pre>
To add Markdown support to a ‘Product’ custom post type, add this to your theme’s functions.php file:
<pre><code>add_post_type_support( 'product', 'wpcom-markdown' );
</code></pre>
<h3>Syntax Highlighting</h3>
By default, Markdown Editor enables syntax highlighting for code blocks. This can be removed by adding the following line of code to your theme’s functions.php file:
<pre><code>add_filter( 'markdown_editor_highlight', '__return_false' );
</code></pre>
The click to copy button can be removed with the following line:
<pre><code>add_filter( 'markdown_editor_clipboard', '__return_false' );
</code></pre>

Markdown Editor

Message emitted - The plugin does not have a valid header.

Kills WordPress

Replaces the default WordPress editor with a Markdown editor for your posts and pages.

MarkdownBar vs Markdown Editor