What is the best business management book?

Some people say....

Microsoft Small Business Kit
http://www.microsoft.com/MSPress/books/7123.asp

According to Amazon the best book on business management is "The Ultimate Competitive Advantage" by by Donald Mitchell, Carol Coles, B. Thomas Golisano

t depends, of course, on what you want to learn from the book.

For example, Peter Drucker is considered the father of modern management theory. He is easy to read and has lots of great insight. Here is a terrific starting place:
http://www.buch-info.net/ISBN/006093574X

You might want something that is a bit more "personal" and I really like the book by Howard Schultz, the founder of Starbucks, called "Pour Your Heart into It".
http://www.buch-info.net/ISBN/0786883561

If you are interested in something like influencing others, as one of the other answers suggests, then the most important book on the topic is by Robert Cialdini, a respected researcher and the world's leading expert on influence and persuasion (it is a great book):
http://www.buch-info.net/ISBN/0688128165
There are lots of others out there. Ask great managers you know to make a recommendation.