Zero to Marketing - Short case studies that help you get better at marketing
Content Marketing Stack - A curated directory of content marketing resources
AppGrowthLab (by SplitMetrics) - 55 app growth lessons from 30 app marketing experts
The Influencer Marketing Stack - Free resources to launch a killer campaign
Kickstart Side Hustle Newsletter - Dwarf-size newsletter with viral marketing case studies
Marketing Examples - A gallery of real world marketing case studies. Updated every day.