Doc.vim is a project mainly written in Vim Script, it's free.
Syntax colouring for ASCII documentation
This is a mirror of http://www.vim.org/scripts/script.php?script_id=262
Gives you syntax coloring for ASCII-documentation files. Not perfect, but may be a base for your own.
Detects headlines (underlined with '-' or '='), enumerations, lists (starting with '-' or '*') some simple time, date formats some simple email addresses, web addresses.