I would like to add my vote for a Marked quick look plugin. One
of the big advantages to using QuickLook is that -- once open --
you can use your arrow keys to navigate through list of files and
QuickLook automatically updates to give you previews for each one.
If you keep multiple Markdown notes in one folder, this is so much
easier than having to open and close each one in separately.
For my own work, I use DevonThink to store... everything. I do a
lot of academic research , so my notes are packed with LaTex code.
Unfortunately, DevonThink lacks a decent preview for LaTex or
Markdown. So for me, something like this would be fantastic!