MailChimp is offering 3 email templates for download on their website. So is you want to design and code your own HTML email newsletters, but aren't really sure where to begin, you can start by downloading them here. I've checked them out myself and the only thing I can say about them is: well done, guys! :)
The templates have been tested in various mail clients and, apart from the html files, the zip file also contains Photoshop, Illustrator and Fireworks files. And as a bonus they've added two helpful resources: a free email design guide and an email application QA checklist. Even the sample templates themselves have tips & tricks as content. I love it!