John Vlissides, Addison Wesley (Software Pattern Series), 0201432935
In some ways, this book feels as the errata chapter of Design Patterns. It adds to the Design Patterns book. On the other hand, Vlissides book has a much nicer narrative form and puts Design Patterns in a more casual perspective, for example by showing some variations to some patterns. The book is somewhat expensive, as it isn’t as definitive or authorative as it’s $30 price tag suggests.