Product School - The global leader in product management training
Intercom on Product Management - The ultimate resource for aspiring product managers
Software Product Management Stack - Resources & tools to help you manage your software product
Getting Real - The smarter way to build web apps. A free book by 37signals.
Intercom - Intercom is a customer relationship management and messaging tool for web businesses. Build relationships with users to create loyal customers.
The Manager's Handbook - Comprehensive guide to becoming a great manager