Here are some of them:
[[[http://stackoverflow.com/questions/2229822/best-practices-considerations-when-writing-html-emails]]]
<p>Getting Started Guides:(from the stackoverflow link above)</p>
<ul>
<li><a href="* [[[http://www.campaignmonitor.com/resources/will-it-work/guidelines/">]]]Campaign Monitor</a></li><li><a href="* [[[http://kb.mailchimp.com/article/how-to-code-html-emails/">]]]Mailchimp</a></li><li><a href="* [[[http://www.sitepoint.com/code-html-email-newsletters/">]]]Sitepoint</a></li><li><a href="* [[[http://www.reachcustomersonline.com/how-to-code-html-email-newsletters-all-new-version/">Reach Customers Online</a></li><li><a href="* [[[http://dev.tutsplus.com/tutorials/what-you-should-know-about-html-email--webdesign-12908">Tuts+</a></li>
</ul>
<p>CSS Support & General Guides:</p>
<ul>
<li><a href="http://www.campaignmonitor.com/css/">Campaign Monitor | CSS Support Guide</a></li>
<li><a href="http://htmlemailboilerplate.com/">HTML Email Boilerplate</a></li>
<li><a href="https://litmus.com/help/email-clients/">Litmus | Email Clients FAQ's</a></li>
<li><a href="http://www.campaignmonitor.com/resources/will-it-work/">Campaign Monitor | Will it work?</a></li>
<li><a href="http://mailchimp.com/resources/guides/email-marketing-field-guide/">Mailchimp | Email Marketing Field Guide</a></li>
</ul>
* [[[http://www.campaignmonitor.com/css/]]]Campaign Monitor | CSS Support Guide* [[[http://htmlemailboilerplate.com/]]]HTML Email Boilerplate* [[[https://litmus.com/help/email-clients/]]]Litmus | Email Clients FAQ's* [[[http://www.campaignmonitor.com/resources/will-it-work/]]]Campaign Monitor | Will it work?* [[[http://mailchimp.com/resources/guides/email-marketing-field-guide/]]]Mailchimp | Email Marketing Field Guide <p>You should always inline your CSS in html-email. Here is a list of <a href="[[[http://stackoverflow.com/questions/791070/what-tools-to-automatically-inline-css-style-to-create-email-html-code/17882057#17882057">]]]CSS Inlining Tools</a></p>
<p>Responsive Guides:</p>
<ul>
<li><a href="http://www.campaignmonitor.com/guides/mobile/">Campaign Monitor | Responsive Support Guide</a></li>
<li><a href="http://stylecampaign.com/blog/2012/10/responsive-email-support/">Style Campaign | Responsive Support Guide</a></li>
<li><a href="https://litmus.com/blog/the-how-to-guide-to-responsive-email-design-infographic">Litmus | Responsive How-To Infographic</a></li>
<li><a href="https://litmus.com/blog/our-favorite-responsive-and-mobile-email-resources">Litmus | Big List of Responsive & Mobile Resources</a></li>
</ul>
* [[[http://www.campaignmonitor.com/guides/mobile/]]]Campaign Monitor | Responsive Support Guide* [[[http://stylecampaign.com/blog/2012/10/responsive-email-support/]]]Style Campaign | Responsive Support Guide* [[[https://litmus.com/blog/the-how-to-guide-to-responsive-email-design-infographic]]]Litmus | Responsive How-To Infographic* [[[https://litmus.com/blog/our-favorite-responsive-and-mobile-email-resources]]]Litmus | Big List of Responsive & Mobile Resources <p>Here is <a href="[[[http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density">]]]a list of devices</a> by resolution and pixel density</p>
<p>Templates & Frameworks:</p>
<ul><li><a href="* [[[http://tedgoas.github.io/Cerberus/">]]]Ted Goas | Cerberus Responsive Email Patterns</a></li><li><a href="* [[[http://www.emailonacid.com/blog/details/C13/emailology_a_free_responsive_email_template_using_media_queries_-_part_i">]]]Email on Acid | Responsive Template</a></li><li><a href="* [[[http://briangraves.github.io/ResponsiveEmailPatterns/">]]]Brian Graves | Responsive Email Patterns</a></li><li><a href="* [[[http://internations.github.io/antwort/">]]]Antwort | Responsive Layouts</a></li><li><a href="* [[[http://zurb.com/ink/templates.php">]]]Zurb | Ink Responsive Templates</a></li><li><a href="* [[[http://www.campaignmonitor.com/templates/all/">]]]Campaign Monitor | Free Email Templates</a></li><li><a href="* [[[https://github.com/mailchimp/Email-Blueprints">]]]Mailchimp | Email Blueprints</a></li></ul>
<p>Responsive Alternate Examples:</p>
<ul><li><a href="* [[[http://stackoverflow.com/questions/20483059/responsive-order-confirmation-emails-for-mobile-devices/20497625#20497625">]]]Stack Overflow | Fluid Example</a></li><li><a href="* [[[https://litmus.com/blog/monsters-fluid-layout-stands-out-among-job-search-emails">]]]Email on Acid | Monster's Fluid Layout</a></li><li><a href="* [[[http://stylecampaign.com/blog/2010/09/fluid-mobile-email-design-part-4/">]]]Style Campaign | Fluid Mobile Email Design</a></li><li><a href="* [[[http://stackoverflow.com/questions/17674172/equivalent-to-float-in-outlook/17677304#17677304">]]]Stack Overflow | Floating Content</a></li></ul>
<p>Also the Ted Goas Responsive link above has an excellent fluid example. </p>
<p>Troubleshooting & General Guides:</p>
<ul>
<li><a href="http://www.emailonacid.com/blog/details/C13/stop_yahoo_mail_from_rendering_your_media_queries">Email on Acid | Yahoo Media Query Bug Workaround</a></li>
<li><a href="http://stackoverflow.com/questions/9697788/html-email-is-colspan-allowed/16964122#16964122">Stack Overflow | Colspans and Rowspans in HTML Email</a></li>
<li><a href="http://templates.mailchimp.com/development/css/outlook-conditional-css">Mailchimp | Outlook Conditional CSS</a></li>
<li><a href="https://litmus.com/blog/update-banning-blue-links-on-ios-devices">Litmus | Banning Blue Hyperlinks</a></li>
<li><a href="http://stackoverflow.com/a/21485767/1435513">Stack Overflow | Webfonts in HTML Email</a></li>
</ul>
* [[[http://www.emailonacid.com/blog/details/C13/stop_yahoo_mail_from_rendering_your_media_queries]]]Email on Acid | Yahoo Media Query Bug Workaround* [[[http://stackoverflow.com/questions/9697788/html-email-is-colspan-allowed/16964122#16964122]]]Stack Overflow | Colspans and Rowspans in HTML Email* [[[http://templates.mailchimp.com/development/css/outlook-conditional-css]]]Mailchimp | Outlook Conditional CSS* [[[https://litmus.com/blog/update-banning-blue-links-on-ios-devices]]]Litmus | Banning Blue Hyperlinks* [[[http://stackoverflow.com/a/21485767/1435513]]]Stack Overflow | Webfonts in HTML Email <p>You'll need to use <a href="[[[http://msdn.microsoft.com/en-us/library/hh846327%28v=vs.85%29.aspx">]]]VML</a> to get background images working in Outlook (Except <a href="[[[http://stackoverflow.com/questions/12970143/how-make-background-image-on-newsletter-in-outlook/13259519#13259519">]]]in the body tag</a>). Here are some VML links:</p>
<ul>
<li><a href="http://backgrounds.cm/">Campaign Monitor | Bulletproof Backgrounds</a></li>
<li><a href="http://buttons.cm/">Campaign Monitor | Bulletproof Buttons</a></li>
</ul>
<* [[[http:/div>/backgrounds.cm/]]]Campaign Monitor | Bulletproof Backgrounds* [[[http://buttons.cm/]]]Campaign Monitor | Bulletproof Buttons