DESIGN PATTERNS, Gamma, Heml, Johnson and Vlissides

This is a must read. I didn't manage to read it in one-go. I haven't even read it all. I find this book hard to read, sometimes hard to understand - but full of great information. I use it as a reference manual, or a catalog.
What I put into practice:
+ Singleton;
+ Facade;
+ Mediator;
+ Observer;
+ Abstract factory;
+ Template method;
+ Adapter;
+ Responsability chain;
+ Proxy;
+ Command;
+ State;
+ Strategy;
+ Visitor;