Markown-Preview is an essential plugin for writing Markdown with Vim. You can preview your markdown file, or just part of it, quickly and easily. You don't even have to convert the file after you seet it, you can just copy from the browser's source and go!
In Vim, type :MarkdownPreview (:MdP for short) to see the rendered results in a browser. You can also choose to preview one small area by selecting it.
Note: multimarkdown is required to be installed.