Really Good Emails - A large collection of good product email design.
BetaList - BetaList provides an overview of upcoming internet startups. Discover and get early access to the future.
Email Love - Email design inspiration, templates and discovery
PitchWall - Browse new startups, and submit your mobile app/games startup's beta page here.
Stripo - Stripo is an all-in-one email design platform. We enable our clients to build emails of any complexity, including interactive AMP emails, really fast and easy.
StartupBase - Community of makers & early adopters