Wake-On-Lan allows you to start up a computer that is turned off. You send a special packet from any computer on the network to the computer that is off. Once the packet has been received it will power up the computer. It is very simple to set up and it doesn't cost you any thing. That's right it free.

Having this configured on my home network has saved me several times. It has saved me walking time, and driving time. For example I always have a computer turned on and configured so I can connect to it from any where in the world. I connect to this computer and then can power up any other computer that is on my home network. So if I need a file off my home computer from work, I can get it in a pinch and my boss is happy.