"The New Market Wizards" by Jack D. Schwager
"Millionaire Traders" by Kathy Lien and Boris Schlossberg
For me, looking into the minds of successful traders and how they work is a great way to learn and gain different perspectives.
"Hedge Fund Masters" by Ari Kiev - A look on how a psychiatrist examines and picks apart top traders psychological weakness and how he would fix them to increase trading performance.
"Enhancing Trader Performance" by Brett N. Steenbarger - Awesome book and unless you have your own trading mentor or coach, this should be read even BEFORE demo trading. Actually, just read it regardless.
"The Complete Turtle Trader" by Michael W. Covel - A great story and a great example on the realities of systematic trend trading. Also, a great study on how psychology affects trading systems.
"Intermarket Analysis: Profiting From Global Market Relationships" by John J. Murphy - definitely required reading for those into fundamental analysis and discretionary trading. A good basis to understand these globalized markets.
These are just a few of the books I've read, but they are some of my favorites as they have had the biggest impact. You may notice that most of them are psychology related in one way or another as I feel understanding yourself is the biggest obstacle to success in trading.
This list will grow over time and I invite everyone to add their favorite books to the list. Thanks!