This website and its sample code creates a template of sorts, absent of design or layout, that will help you avoid some of the major rendering problems with the most common email clients out there — Gmail, Outlook, Yahoo Mail, etc. While not plug and play (you know, you'll have to do some work ;-), it will provide some helpful examples and snippets that will keep your email design rendering as true-to-form as possible.

… a Beautiful Boilerplate for Responsive, Mobile-Friendly Development […] a small collection of CSS & JS files that can help you rapidly develop sites that look beautiful at any size, be it a 17" laptop screen or an iPhone.

(Free Themes Directory)

Just another awesome WordPress.com theme

… an Automattic-produced theme designed and developed by the Theme Team which, apart from the custom possibilities you’re acquainted with in most of our themes — features like custom backgrounds, headers, and menus — is also equipped with a custom Showcase Page Template that can propel your site up to a new level.

«[…] here are 24 total resources that will show you how to design and code Wordpress themes from scratch. This includes 9 design and coding tutorials, 12 Photoshop mockups, 2 Wordpress e-books, and even a developers “Cheat Sheet”.»

Photoshop file that has a fairly comprehensive library of assets – all fully editable

Free design resources layered PSD, resizable vectors, PNG icons