Mentory - On demand career mentors to succeed at work.
PM Starter Pack - Practical guide on how to get started in product management
Tribe of Mentors - Short life advice from the best in the world, by Tim Ferriss
Product School - The global leader in product management training
MentSpot - Find a mentor or become one for free
know/how Product Managers - A weekly newsletter with 5 practical tweet-length PM tips