Early Stage Founders Playbook - Rated 5 out of 5 by indie-hackers and techie founders who love building features and feel hesitant about marketing.
Really Good Emails - A large collection of good product email design.
IndieEarnr - 580+ Affiliate Programs for Indie Hackers & Creators
Good Sales Emails - Best sales emails from great companies
Clever - syncing between education applications for K-12 schools
Great Email Copy - A dose of emails from around the web.