An absurdly simple script that renders your markdown to html.
Update: The latest and greatest version of this tool is markdownd. It contains many improvements, including the ability to watch for changes to your markdown files and automatically update them in a browser. It's also distributed as a binary and doesn't require Ruby.
Markdown Doctor uses pygments for syntax highlighting code blocks.
$ gem install markdown_doctor
Note: You'll also need Python installed on your system.
To output to stdout:
$ markdown_doctor <filename>
To read from stdin and output to stdout:
$ cat "this is a test" | markdown_doctor
To display in a browser:
$ gem install bcat
$ markdown_doctor.rb <filename> | bcat
Try putting this in your .vimrc:
" Quickly display a markdown preview of the current buffer
:map <leader>m :%w ! markdown_doctor \| bcat<CR><CR>