Developing static HTML emails is a pain in the butt. For best results, you need to inline all of your styles at HTML attributes instead of using real CSS (externally or inline). You also typically find yourself being very repetitive with your markup if you have a bunch of static emails that share common elements.
MailMatic to the rescue.
MailMatic is a Ruby gem, that is really just a mashup of tools, that aims to ease the burden of creating and maintaining static HTML emails. It uses StaticMatic, Haml, Sass, and Compass to let you author your HTML emails with all of the facilities you enjoy while creating your dynamic site: templates, partials, helper functions, inline Ruby code, reuse of markup and styles, etc. It uses Premailer to convert the HTML/CSS generated from Haml/Sass into self-contained HTML files that inline all of their styles. Premailer even gives you warnings about styles that may not work nicely in certain email readers.
Armed with this, you can accelerate your ability to crank out static HTML emails, and lessen the burden of maintaining them.
To get started with MailMatic, check out its installation and usage instructions on github at: https://github.com/scottwb/mailmatic.