This my new project. I added a relay (should be 12v, mine is 24 but works fine) to my computer's power supply in order to cut the power to my monitor (or anything plugged to the power supply's 110\220v output, maybe I'l do an outlet to plug my speakers' power supply to, or maybe I'l connect them directly to the computer's power supply) when the computer turns off and turn it back on with the computer, saving electricity and time. All you need is a relay (12v or 5v) that works with 220v (or 110v if it's your mains voltage), a soldering iron with solder, a hot glue gun with hot glue sticks and basic tools (screwdrivers, pliers, etc.)
This works becouse when the computer turns on it will turn on the 12v line on the power supply, which will complete the circuit and turn on the monitor, and when the computer turns off the opposite happens.
Sorry for my english accent (I'm portuguese, although I sound a bit russian) and I also apologise for this video not to be step by step. I was originally going to make it step by step but I acidentaly erased the videos after building this.