SnakeLogic - The puzzle based snake game
Product School - The global leader in product management training
Gumroad Small Product Lab - Bite-sized lessons to help you launch your product.
The Product Manifesto - Product Managers face the biggest challenges of our day, which is why our community needs a common set of product principles.
Productbox - Talk with fellow product managers about how you do stuff.
Intercom on Product Management - The ultimate resource for aspiring product managers