No blog about design can avoid mentioning GoF's book. It took the world by storm in the middle 90s and little by little it percolated to mainstream programming. After it there are JEE patterns, distributed patterns, enterprise patterns ... you name it.
Gof's comes from the Smalltalk tradition and shows how to add flexibility to class-based OO languages like C++ and Java. Gof's defines a common vocabulary and typical design solutions for some problems (based on the architectural work of Alexander). In this century critics have reacted to this, despising (with reason) those who use patterns like recipes (see Kerivesky's work for a reasonable alternative) and languages who need these patterns as "broken" (partly true). Newer languages based on the class-based OO tradition have tried to simplify or directly implement as idioms these patterns. Gof's is a book EVERY designer should read and understand, anyway.
I'll enumerate (with some notes) all Gof patterns (and some more here). I'll try to show some Scala implementation of these patterns as a personal exercise. UML 2 tries to simplify pattern representation (aiding to represent other high-level multiclass 'packages'). There is a nice (if slighty mocking) pseudo elements table relating them (worth printing to despise unknowing 'hackers').
Creational
These are patterns that try to simplify and generalize object creation strategies.
Singleton; Factory Method; Abstract Factory; Builder; Prototype
Structural
These help building common object structures.
Adapter; Decorator; Façade; Bridge; Composite; Flyweight; Proxy
Behavioral Patterns
These help building common collaboration patterns.
Chain of Responsibility; Visitor; Observer; Iterator; Mediator;State; Command; Mememto; Strategy
And, finally Gof includes a pseudojoke to help remember that no 'static' language is sacred and that scripting is usually needed: Interpreter.
Great book, (not the last word) but a common ground for OO developers.
Also check: JEE patterns, enterprise patterns, analysis patterns, ...
