Newsletters are a great marketing tool. Even in this age of mountains of spam and solutions like RSS, people continue to subscribe and well implemented campaings continue to convert. Below you can find tips and tricks to newsletter marketing and some tools for managing and sending out your e-mails.
I don't like adding "for year xxxx" stuff to the resources very much, but these tips should hold up for longer than just next year :-). Some of this seems obvious enough, but you would be surprised how many newsletters I get that don't account for images being turned off and the preview pane, for example.
A sequel to CSS and Email, Kissing in a Tree from Alistapart, this blog post from the super-helpful Campaign Monitor weblog helps demystify a few more issues of building a successful e-mail newsletter.
Concluding that HTML emails that contain semantic markup and CSS fare very well with the most commonly used email clients
this article helps to clean up traditionally ugly newsletter markup, and has example files available for download.