Forum user pighixxx has created a fantastic PDF "booklet" available for free download:
http://www.pighixxx.com/abc-arduino-basic-connections/
It currently consists of 35 colour pages showing sample circuits, plus 4 pages of reference material (resistor and capacitor component markings).
There are examples of connecting lots of types of circuits: push buttons, opto couplers, photo resistors, relays, speakers, microphones, level converters, MIDI interface, LCD screens, rain sensors, IR sensors, IR transmitters, and much more.
Examples of his style:
Whether you are new to electronics and Arduinos, or experienced, this is a very useful reference.
The document is released in "sets" of 3 pages each (to reduce download time).
Currently they are:
Page 1
- Pushbutton (switch)
- Trimmer/potentiometer
- Photo resistor
- Optocoupler inputs
Page 2
- LEDs
- Dual-colour LEDs
- LED clusters
- Lamps
Page 3
- Relay
- Audio amplifier
- MOSFET
- Buzzer
Page 4
- Speaker
- Triac
Page 5
- RGB LED strip
- DC motor
- Rotary encoder
Page 6
- Bi-Directional Voltage Level Converter 3.3V to 5V
- Bi-Directional Voltage Level Converter 3.3V to 5V with voltage divider
- TTL / CMOS converter (6 inputs/outputs)
- TTL / CMOS converter (with transistor)
Page 7
- Microphone
- Servo
Page 8
- Charlieplexing
- 7 Segments Display
Page 9
- 7 Segments Display (Common Anode) with Multiplexing
- LED Array
Page 10
- 7 Segments Display (Common Anode) with MAX7221
Page 11
- LCD HITACHI 44780 compatible
Page 12
- LCD HITACHI 44780 compatible via I2C
Page 13
- NOKIA LCD (Basic)
Page 14
- Drive a Unipolar Stepper
Page 15
- Graphical LCD via I2C
Page 16
- Simple 5V Power Supply
- DIY Arduino
- FTDI Connector
- Protect a I/O Pin
- ICSP pinouts
Page 17
- SD card
- Simple 3.3V Power Supply
Page 18
- Temperature Sensor (LM35)
- RTC (Real Time Clock) (DS1307)
- Composite Video
- VGA Video
Page 19
- Keypad
- Keypad with interrupt
Page 20
- IR sensor
- IR emitter
Page 21
- MAX232 (RS232 level converter)
Page 22
- MIDI Interface
- Multiple Buttons using 1 Analog Input
Page 23
- Digital Temperature Sensor (DS18B20)
- A simple Rain Sensor
- AC input
Page 24
- PS2 keyboard
Page 25
- EEPROM via I2C
Page 26
- PS2 Dualshock® controller
- A Simple programmer
Page 27
- Port Expander (PCF8574xx)
- How to connect multiple port expanders
Page 28
- Shift register
- How to connect multiple shift registers
Page 29
- Distance Sensor (Sharp GP2Y0A21)
- Digital Potentiometer (MCP4161)
- DAC (MCP4921)
Page 30
- RS485 Node
- DMX Controller (Basic)
Page 31
- Drive a Motor (L298)
Page 32
- Debouncing a Pushbutton
- Simple Debouncer
- Debouncing a Rotary Encoder
Page 33
- Drive a Stepper (L293)
Page 34
- Logic analyzer
- Current sense
Page 35
- Component Tester (basic)
Page 36
- (Work in progress)
Page I
- Resistor colour codes
Page II
- Ceramic Capacitor Codes
Page III
- Polyester Film-Mylar Capacitor Codes
Page IV
- Simple Transistor Comparison Table
Page V
- (Work in progress)
Page VI
- (Work in progress)
Check his site for updates, more pages may be released which are not listed above.