Everything listed here are things I believe, have used, and highly recommend.

Must Read Books for everyone:
The 7 Habits of Highly Effective People by Stephen Covey
Who Moved My Cheese by Spencer Johnson
Start With Why by Simon Sinek

For New Leaders:
Welcome to Management by Ryan Hawk

For those trying to take team to next level:
The 4 Disciplines of Execution by Chris McChesney

Best Stock Trading Site: Robinhood.com (Read my article here)