Apple - iPod Touch Review

Ambient Light Sensor
The iPod touch display has an ambient light sensor that automatically adjusts brightness to suit the ambient light in your surroundings. The result? A better experience for you and battery-saving efficiency for iPod touch.

Accelerometer
An accelerometer detects when you rotate iPod touch from portrait to landscape, then automatically changes the contents of the display, so you immediately see the entire width of a web page, your music in Cover Flow, or a photo in its proper aspect ratio.