For convenience, this is a quick list of great resources I find insightful.

Pollenizer – Lean Startup Tools
Pollenizer – Universal Startup Pitch Deck
SaaS Blog – Chaotic Flow – Invaluable Insights
Seth Godin’s Startup School
Startup Owner’s Manual – by Steve Blank and Bob Dorf

Professional Development:
Winning Arguments – by Jay Heinrichs
Power: Why Some People Have It and Others Don’t – by Jeffrey Pfeffer

Business Books for Entrepreneurs

The Knack: How Street-Smart Entrepreneurs Learn to Handle Whatever Comes Up – by Norm Brodsky and Bo Burlingham
The New Business Road Test – by John W. Mullins
Financial Intelligence for Entrepreneurs – by Karen Berman and Joe Knight

Agile Software Development / Project Management:

Personal Kanban
The Elements of Scrum – by Chris Sims