Uberwriter is a Linux-only, Ubuntu-based markdown editor with some strong export options (odt, pdf, epub, rtf, html, latex source, MediaWikie markup). It sells for $5.
Other features inclue:
- 'Focus' Mode greys out all but the sentence you are actively working on.
- Fullscreen Mode
- Inline Markdown Highlighting
- Live Word and Character counting
- Out of the box math support.
I haven't tried it, but it seems a useful tool, and maybe the only Linux markdown editor of note at this writing.