Tutorials
Sparkfun's tutorials go from the Arduino Assembly Guide, a Quick Start Guide to get you using an Arduino through guides for a host of add on "shields" made for all sorts of things.
The Arduino tutorials show you have to do all sorts of things with the Arduino - with the "sketches" to go with them - and explanations of what and how each one does what it does.
Lady Ada Tutorials - six lessons the start with a pref-flight check and cover switches, buttons, digital inputs etc. Great Step By Step - with sample screens, photos of steps, "sketches" with explanations of what's doing what.