Stripo - Stripo is an all-in-one email design platform. We enable our clients to build emails of any complexity, including interactive AMP emails, really fast and easy.
Really Good Emails - A large collection of good product email design.
MJML - The open source framework for responsive emails
Email Kick - Email designer and analytics for your transactional emails.
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Startup Emails - Responsive HTML email templates for startups