Analogue Gauge with Arduino
The simplest analog gauge is an ammeter.  Connect one end to an analog output pin, the other to the middle pin of a potentiometer, and another pin of the pot to ground.  You'll need to tweak the potentiometer to calibrate the range of the output.  Make sure that you measure the resistance across the ammeter and don't short out the arduino's output pin.  You can use analogWrite() to move the needle.