8760 Hours in a year. Call it 10,000 for easy reckoning. Energy 10p per Kwh. I know it's gone up more than that, but it illustrates the point. That means 1 watt of energy for 1 year costs 1 pound. So add up all the power consumption figures in watts. Things like TV's and DVD's manuals often give the power consumption in standby. That total figure is ( was at around 10p/Kwh ) the amount in pounds per year, very approximately.
Laurie53 don't take it personally but why does anyone leave their PC on all the time? When asleep or out they can't read mail chat etc.
Turn it off completely including the transformers for your amps, speakers, scanner, printers, screen, backup drives etc. This will reduce your costs and reduce the need for more power stations that feed all these items on standby.
Note to that leaving your network on 24 hours a day is asking for trouble as your IP address will be static and hackers have all day to break down your defenses.