Every one knows accelerometers from Wii controllers and smart phones. Being fairly inexpensive, they’re a prime candidate for including in a DIY project. I’ll detail how to hook up a Memsic 2125 (most common) dual-axis accelerometer and measure its tilt in this post.
An IR receiver can detect infrared light emitted from an IR LED. This post details how to hook up both parts as well as detect a break in the signal between the two, which would allow you to tell if something passed between them.
A Servo, short for “servomechanism”, can rotate 180 or continuous 360 (depending on the type). Servos consist of a motor & a potentiometer and can easily be hooked up to an Arduino. This post details how.
A slide switch can be used to toggle power on and off. This post will detail how to use a slide switch with a 9V battery and your Arduino.
Photo resistors measure light. The amount of light varies the resistance and determines a value between 0 and 1023. This post details how to hook one up to an Arduino.
A thermistor, or thermal resistor, can detect temperature since it’s resistance will vary depending on the temperature. This post will detect how to wire a thermistor to an Arduino as well as code to read a Fahrenheit value from it.
A potentiometer is basically just a dial. Depending on its rotation, it will read in a value between 0 and 1023 to use in your Arduino program. This post details how to hook up a potentiometer to an Arduino.
A soft pot works just like a regular potentiometer; however, instead of turning a dial, you slide (your finger) up and down the strip to change the values. This post details how to hook up to an Arduino.
Buzzers allow for simple audio output. Running them at different speeds allow for a variety of tones. This post details how to hook one up to an Arduino.
A button is a simple switch with 2 values: on or off, which is 1 or 0 respectively. No surprise there. This post details how to hook it up and read its value into your Arduino program.