Impact the type of service and tools you will use
Getting Started With HTML EMails
SMTP Authentication Support Module
Structure of HTML email
Create E-mails content
Mime Mail
Allows for email attachments
Mandrill / Mail System
Can setup rules (within the Mandrill service) to change e-mail attributes before sending
HTML E-mails From Outside of Drupal (List Signup Only)
Use site content to build newsletters
Constant Contact
Some E-commerce and Webform integration
Campaign Monitor
Easy template generation
Zurb Foundation
Module of the week Table Field - https://www.drupal.org/project/tablefield
This module allows you to attach tabular data to a node in Drupal 6 or any entity in Drupal 7. The input form allows the user to specify the number of rows/columns and allows entry into each table cell using text fields. Tables can be defined globally or on a per-node/per-entity basis, so every node can have multiple tables of arbitrary size. Enter data by hand or by CSV upload. Table data can also be downloaded as CSV files by your users if you so choose. Tables are multi-value and revision capable.
Resources Simple News - https://www.drupal.org/project/simplenews
Mime Mail - https://www.drupal.org/project/mimemail
SMTP Authentication Support Module - https://www.drupal.org/project/smtp
Mandrill - https://www.drupal.org/project/mandrill
Mail Tester - http://www.mail-tester.com
Mail System - https://www.drupal.org/project/mailsystem
Mailchimp - https://www.drupal.org/project/mailchimp
Constant Contact - https://www.drupal.org/project/constant_contact
Campiagn Monitor - https://www.drupal.org/project/campaignmonitor
Responsive Email Design from Campaign Monitor - http://bit.ly/rt-rdemailcm
Web Fonts in Email from Campaign Monitor - http://bit.ly/rt-emailcm
Responsive Email from MailChimp - http://bit.ly/rt-rdemailmc
Typography in Email from MailChimp -http://bit.ly/rt-emailmc
Tutorial to Understand HTML Email (Hand crafted) - http://webdesign.tutsplus.com/articles/build-an-html-email-template-from-scratch--webdesign-12770