Richard Stanley's two-volume basic introduction to enumerative combinatorics has become the standard guide to the topic for students and experts alike. This second edition includes more than 300 new exercises, many with solutions, updated and expanded chapter bibliographies and substantial new material on permutation statistics.
This is my current favorite bathroom literature (my copy of Weisstein's Encyclopedia of mathematics is tucked away somewhere in my ex-gf's cellar) The info density of this book is just incredible!
Awesome textbook. This book is meant to be "read" with pencil and paper in hand. The presentation clearly comes from an author who just loves to "count", and is an expert at it.