If you work a lot with markdown files in OS X, previewing them can be difficult as the finder's quicklook option doesn't render out markdown.
Phil Toland has provided a plug-in for quicklook to render out the markdown.
- Download the latest version of QLmarkdown
- Extract the QLMarkdown.qlgenerator file to ~/Library/QuickLook. Create the directory if needed.
- Relaunch Finder