Great idea for a thread.
There are so many from guys like Seth Godin, Gary Vaynerchuk, etc. I'll throw down the one's that I keep returning to;
Ego is the Enemy - Ryan Holiday
Ryan has written a good few "business" books now. This one is about keeping your head together as you make your way through your career (up or down).
The War of Art - Steven Pressfield
For the creatives this one is a must.
Unlabel: Selling You Without Selling Out - Marc Ecko
Business from an initial love, to making money with that, to selling the business that you've built upon yourself.
Steal Like an Artist - Austin Kleon
Another creatives one. Just read it, it's fairly cheap and if it doesn't inspire you to make something then you need to see a doctor.