Org-mode is my markup of choice. I spend the vast majority of my time working on text files working in org-mode. Since GitHUb started rendering org-mode files in their site I've also used org-mode for things like Readme files in my projects. I even force it on my students at times. When I make an assignment, I seed it with an org-mode file that they have to modify - that is - fill in things like their names, group members etc..
That said, sometimes I have to work in plain old markdown. This is almost always when I'm working on something collaboratively and more often than not it's documentation on a project living on GitHub.
So, given that I have to work with Markdown, time to use some Emacs magic to make it easy and fun.
You can check out the video to see grip-mode along with some of the other modes I tried here: