The MaxSonar EZ1 provides very short to long-range detection and ranging, in an incredibly small package. It can detect objects from 0-inches to 254-inches (6.45-meters) and provides sonar range information from 6-inches out to 254-inches with 1-inch resolution. (Objects from 0 inches to 6-inches range as 6-inches.) The interface output formats included are pulse width output (PWM), analog voltage output (Vcc/512 volts per inch), and serial digital output (9600 baud).
A good sensor for when a Sharp IR distance sensor won’t cut it. For example of using this with an Arduino, see the Halloween Pumpkin project. Much more information is available in the datasheet. In the Adafruit store now!
Tilt ball switch – The “poor man’s” accelerometer! Tilt sensors are switches that can detect basic motion/orientation. The metal tube has a little metal ball that rolls around in it, when its tilted upright, the ball rolls onto the contacts sticking out of end and shorts them together. There’s no datasheet but they’re fairly easy to use! In the store now!