Templates by Email Monster - Hundreds of free, responsive email templates. Pick and edit.
PandaDoc for Developers - PandaDoc for Developers — easy and scalable all-in-one API solution for generating documents and capturing eSignatures by embedding them into your app, website, or using the backend API.
Really Good Emails - A large collection of good product email design.
Presentation templates by Pitch - Designed for big ideas and customizable for any story
Good Email Copy - Email copy from great companies.
Creodocs - Make consistent business documents from beautiful templates