This AT407 basic tilt switch can easily be used to detect orientation. Inside the can is a ball that make contact with the pins when the case is upright. Tilt the case over and the balls don’t touch, thus not making a connection.
There are numerous uses for these basic sensors, but keep in mind you might need to use some [debouncing code](http://arduino.cc/en/Tutorial/Debounce), as the sensor isn’t immune to small vibrations and such.
* [GitHub](https://github.com/sparkfun/AT407_Tilt_Sensor) (Firmware)