I had this remote control module (basically a garage door opener) lying around so I decided to put it into use
This module has two relays and each of them is controlled by the corresponding button on the remote control.
I wired the relays in series, so both buttons on the remote have to be pressed simultaneously to turn the computer on.
I also had to make a little boost converter, because the module runs on 12V and I wanted to power it from the motherboard's 5VSB supply.
For more info see the article here:
http://fubar.gr/remote-controlled-computer-power-on-eng/The Youtube video has English captions available.