List of Sensors and actors, connectable to the Arduino Board - categorized by physical effects. - feel free to add ideas or comments to each section or create a new section.
Moisture
moisture++: pump moisture--: heat, pump,
Vibration
Sensor: piezo Actor: vibration motor, all kinds of motors, speakers, many mechanical actors
Temperature
Resistive Sensor, All kinds of electric heating like Toaster,
Sound
Audible Toys, Keyboards, Audio players, Generated Audio on Arduino
microphone: dynamic, piezo, capacitive (electrete capsule) actor: speakers, motors,
(Air) pressure
sensor: microphone, bend sensors on flexible surface, vacuum cleaner, fans, balloon pumps, hair drier
Air movement
air speed measurement fan, hair drier,
Light
LED, computer screens, bulbs, photo flashes,
Graphical output / Displays
LED 7 segment display, LCD, TFT, hacked video signal, data projector, overhead projector with changing image, slide projector
Rotation
Motors, Fans, Servo, Stepper Motor, DC / Brushless Motors, Hard drive Sensors: light barrier, frequency measurement: magnet (reed-contact) rotary encoder, video analysis,
Linear movement - push - pull
Solenoids, Linear motor, Motor with belt or bolt + nut, CD-Rom, toy cars, toy railway, Printers, Scanners
distance sensors: optical, pedometer, acoustic (ultrasonic / audible), hacked optical ps/2 mouse
Position (2D)
radio controlled Toys, displays, object moved by air movement, ...
Radio
AM or FM transmitter AM or FM receiver