Arduino examples, tutorials, and documentation elsewhere on the web.
Books and Manuals
Getting Started With Arduino (by Massimo Banzi): It's a guide for absolute beginners that takes you through the basic steps of learning how to use Arduino.
Making Things Talk (by Tom Igoe): teaches you how to get your creations to communicate with one another by forming networks of smart devices that carry on conversations with you and your environment.
Additional documentation has been created by the Arduino community on the publicly-editable playground wiki.
Other Examples and Tutorials
Arduino 101 videos from Make (part of the How-To-Tuesday series):
Tom Igoe's Physical Computing Site: lots of information on electronics, microcontrollers, sensors, actuators, books, etc.
Spooky Arduino: Longer presentation-format documents introducing Arduino from a Halloween hacking class taught by TodBot:
Bionic Arduino: another Arduino class from TodBot, this one focusing on physical sensing and making motion.
Fritzing: an open source electronic circuit diagramming tool designed for users not previously familiar with electronic schematic diagrams.
Schematics to circuits: from Wiring, a guide to transforming circuit diagrams into physical circuits.