Design patterns: common, reusable life savers for developers that don’t want to reinvent the wheel. If you haven’t familiarized yourself with this essential piece of software engineering, add it to your knowledge queue!
Jason McDonald did a great job summarizing the meaty bits of Design Patterns: Elements of Reusable Object-Oriented Software into a neat, UML-formatted quick reference chart. Download it here for free
Or if you prefer a more in-depth look, check out the book on Amazon.com