Finance for Non-Financial Managers A good solid reference book that is easily understood at a practical level for applying financial concepts.
Understanding Financial Statements by Lyn Fraser & Aileen Ormiston An accounting textbook, but readable and useable.
Common Stocks and Uncommon Profits by Philip A Fisher A book recommended by The Motley Fool for deciphering company and stock performance.
The Portable MBA A great reference book which shows examples of how financial concepts are put to use. It also discusses current management philosophies. What Every CEO Wants You to Know by Ram Charon A short readable book about the concept of "business acumen." It emphasizes that underneath it all, every company looks the same in terms of business concept.