"How to Win Friends & Influence People" - Dale Carnegie
It's been a best-seller for 70+ years and Warren Buffett openly admits that when he was young he, read and reread this book many times.
48 Laws of Power
One of the most interesting and valuable books I have ever read. Basically shows you techniques to get, win, take, steal ... anything you want.
The richest man in babylon. If you are a fan of King James english an ye olde style stories, this is a great read. If you aren't fond of reading, get a .mp3 of the book.
Four Hour Workweek - Tim Ferriss