This project contains the style sheet I use for Multimarkdown documents as well as an example document that provides a good base of content to work with when testing new styles. For fun, I incorporated the Lobster font from the Google Font Directory for the headings.
First you'll need to install Multimarkdown. See the site for instructions on how to do that.
You'll also need the TextMate bundle to generate the previews using MMD and not the built in Markdown
To use the style sheet simple link to it in the meta section of your markdown file. See the example for details
CSS: http://github.com/btoone/mmd-stylesheet/raw/master/mmd.css
My workflow is to edit a MMD file in TextMate and the preview it (ctrl + opt + cmd + p). This renders the MMD file as HTML and uses the linked style sheet. However there are several ways to render the HTML, see the MMD site for details.
You can see the generated HTML by downloading this example