I’m sure this is going to seem trivial, but I spent way too much time looking for a way to convert my emacs org-mode notes into (github flavored) markdown. You see, I’ve been an emacs user for so long, that I assumed the only way to do it was from within emacs, but I finally found pandoc. So trivially:

pandoc --from=org --to=gfm org-mode-file.org > markdown.md

For more options, check out the Pandoc Manual.

In case you are wondering, I’ve finally gotten off of emacs and switched to atom. I still use the emacs style keybindings, as my hands are faster that way.