Here you will find a growing number of examples and tutorials for accomplishing specific tasks or interfacing to other hardware and software with Arduino. For instructions on getting the board and environment up and running, see the Arduino guide.
Simple programs that demonstrate the use of the Arduino board. These are included with the Arduino environment; to open them, click the Open button on the toolbar and look in the examples folder. (If you're looking for an older example, check the Arduino 0007 tutorials page.)
These examples include code that allows the Arduino to talk to Processing sketches running on the computer. For more information or to download Processing, see processing.org.
These are more complex examples for using particular electronic components or accomplishing specific tasks. The code is included in the tutorial.
Interfacing w/ Hardware
Tutorials created by the Arduino community. Hosted on the publicly-editable playground wiki.
Interfacing With Hardware: Code, circuits, and instructions for using various electronic components with an Arduino board.
Interfacing with Software: how to get an Arduino board talking to software running on the computer (e.g. Processing, PD, Flash, Max/MSP).
Code Library and Tutorials: Arduino functions for performing specific tasks and other programming tutorials.
Electronics Techniques: tutorials on soldering and other electronics resources.
Manuals, Curricula, and Other Resources
Arduino Booklet (pdf): an illustrated guide to the philosophy and practice of Arduino.
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.