Transactional Email Templates by Postmark - Open source email templates for use in your SaaS app.
SaaS Email Templates - Responsive HTML email templates for SaaS startups
Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
Email2Go.io - Perfect emails are born here
Email Template Generator - Email templates for your important relationships
Great Email Templates - HubSpot email templates for SaaS marketers