The Circuit Playground board from Adafruit is a wonderful thing. It provides a self contained learning environment for Arduino with built-in environmental sensors, neopixels, and buttons and switches in a wearable format for $20. This is an excellent teaching tool that is cheap enough for students to take home with them and continue tinkering with. The board is event built into the current Arduino environment.
I have developed a introductory workshop to the Arduino world using the Circuit Playground. At the moment I am offering this workshop at the Columbus Idea Foundry. Materials for the course can be found under the workshop tab on this site.