Today, something easy : lets use a SD Card Reader with our arduino.
Can be useful for instance when you want to log datas such as temperatures or any other sensor.
I use this component from DS : SD Card Slot Socket Reader.
First the wiring : standard SPI (SCK/MOSI/MISO/CS).
Then some arduino skeches taken from the Arduino examples (note that I use CS=10 with my arduino uno, adapt if needed) :
That was it : quick and easy !