Content Marketing Stack - A curated directory of content marketing resources
Really Good Emails - A large collection of good product email design.
GrowthHackingIdea.com - One short, curated growth hacking idea a day to your email
Good Sales Emails - Best sales emails from great companies
This Won't Scale by Drift - 40 free marketing playbooks to help you grow your business
Great Email Copy - A dose of emails from around the web.