Really Good Emails - A large collection of good product email design.
Facebook for Business - Facebook Business gives the latest news, advertising tips, best practices and case studies to meet the business goals.
Email Love - Email design inspiration, templates and discovery
SocialPilot - SocialPilot is an app designed to help businesses and professionals with social media marketing.
Stamplia - High converting and beautifully designed email templates
Buzzstream - Build Relationships. Build Buzz. Web-based software that helps the world’s best marketers promote their products, services and content.