MultiMarkdown Composer is a text editor for Mac OS X, designed from the ground up around the MultiMarkdown Syntax. It is designed to make writing in Markdown even easier, with automatic syntax highlighting, built-in previews and easy exporting to any format, so you can focus on actual writing, rather than worrying about formatting and styles.
I love Markdown, because it formats text easily in HTML, PDF, RTF and more. Just write your document with minimal formatting, and use the text in any way you choose.
This article gives you a slew of options -- some of which will be new to you as they are to me -- to make your writing life easier.