Ask HN: What do I want to start hacking Arduino?

This weekend, I've been looking at what I'll need to jump into Arduino. I'm looking for list of things above and beyond the bare minimum. I would like to have a kit that will put me in a good position to explore Arduino's possibilities and will be able to keep me busy for a little bit.

I've found this that is along the lines of what I'm looking for: http://www.ladyada.net/learn/arduino/

Any thoughts?