Amazon.com
Design Patterns is a modern classic in the literature of object-oriented development, offering timeless and elegant solutions to common problems in software design. It describes patterns for managing object creation, composing objects into larger structures, and coordinating control flow between objects. The book provides numerous examples where using composition rather than inheritance can improve the reusability and flexibility of code. Note, though, that it's not a tutorial but a catalog that you can use to find an object-oriented design pattern that's appropriate for the needs of your particular application--a selection for virtuoso programmers who appreciate (or require) consistent, well-engineered object-oriented designs.

From the Preface
This book isn't an introduction to object-oriented technology or design. Many books already do a good job of that...this isn't an advanced treatise either. It's a book of design patterns that describe simple and elegant solutions to specific problems in object-oriented software design....Once you understand the design patterns and have had an "Aha!" (and not just a "Huh?" experience with them, you won't ever think about object-oriented design in the same way. You'll have insights that can make your own designs more flexible, modular, reusable, and understandable--which is why you're interested in object-oriented technology in the first place, right?