Divides people by the type of income they predominantly make. Great read. Ignore all the others that were written after this book. Also I would ignore his advice about network marketing, it's a scam IMO.
Managing Oneself by Peter F. Drucker — We live in an age of unprecedented opportunity: If you’ve got ambition and smarts, you can rise to the top of your chosen profession, regardless of where you started out. But with opportunity comes responsibility. Companies today aren’t managing their employees’ careers; knowledge workers must, effectively, be their own chief executive officers. It’s up to you.