The following are three great sites I found about the topic.

Huston Design Patterns. It contains demos and examples (in C++ and Java) to explain various design patterns. A good resource for learning by example.

The Design Patterns Java Companion is a free online book on Java Design Patterns. The author, James W. Cooper, is a Research Staff Member in the Information Retrieval and Analysis group of IBM Thomas J Watson Research Center. The book was published in 1998 and 218 pages in length.

Design Patterns, a Java resource from cs.rice.edu. The pattern discussions, except for the Null and Model-View-Controller patterns are adapted from the classic text, Design Patterns by Gamma, Helm, Johnson and Vlissides (Addison Wesley Longman, 1995. ISBN 0-201-63361-2)

Design patterns form a cohesive language that can be used to describe classic solutions to common object oriented design problems. These patterns enable us to discuss systems of objects as quasi-encapsulated entities. By using design patterns to solve programming problems, the proper perspective on the design process can be maintained.