This week I used an Arduino and my PC to clone an infrared remote control. I used this to automatically turn on an electric heater every morning so my bedroom is nice and toasty when I wake up!
Download the code: http://www.richardosgood.com/blog/wp-content/uploads/2013/11/ArduinoInfraredCloner.zip
Much of the Arduino code was borrowed from Adafruit.com's IR Decoder examples. Be sure to check them out if you do a lot of electronics projects!