Integrated Markdown WYSIWYG text editor
SimpleMDE, a newcomer, may be the answer. I've been searching for something just like this for a month now. I'm surprised that this does not show up higher in search results. I had to go through a notice on lepture/editor to find this.
I was researching in this subject the other day and I haven't found any decent WYSIWYG editor with Markdown output. In fact, first you have to have to create a WYSIWG Markdown editor is WYSIWG HTML editor and there are just few of them that are usable on the market.
There's a chance that you'll be able to create dataProcessor
for CKEditor that will change HTML editor into Markdown editor. We've got a plugin for BBCode that works like this (check out http://nightly-v4.ckeditor.com/3737/samples/bbcode.html).
All you have to do is implement this interface http://nightly-v4.ckeditor.com/ckeditor_api/#!/api/CKEDITOR.dataProcessor. If you check BBCode plugin's code you'll see some hacks and tricks, because unfortunately current CKEditor's architecture isn't ready (yet) to create such a data processor. However, I believe that if you want to provide only few styling options you should be able to implement Markdown support pretty quickly.