Markdown Pro
I am also the author of Markdown Pro, the best markdown text editor for Mac OS X, providing real live-preview as you type and create your document, plus some elegant themes to preview your editing.
You can find Engadget review here: http://www.engadget.com/2014/04/25/apps-we-actually-use-markdown-pro-for-editing-text-and-markdown/
You can download it here