Patterns are very common nowadays and everybody at least has experience with a Factory, an Iterator (duh..), a Facade or a Singleton.
It wasn't always like that. The book that got it all started is called "design patterns", by Gamma, Helm, Johnson and Vlissides. I tried to read it, but the book just wasn't for me.
But now I found a more readable and fun source that discusses patterns. Via an article about the Google singleton detector (“singletons are evil and need to be destroyed”) I arrived at this pattern index by Cunningham & Cunningham. It is a great collection with many funny and serious patterns in all sorts of categories. I particularly like to read the organizational patterns and anti-patterns.