If you haven’t heard of the DZone Refcardz and you are a developer, consider this your Christmas present. From me to you. DZone has been producing those little cheat sheets for a while now and they have built up a pretty nice collection. Each refcard contains a condensed overview of a certain piece of technology or paradigm. In most cases, they can serve both as starting point if you want to learn or as a reference if you already know your stuff.