A little while ago I bought an Energy Saving Smart Strip With Autoswitching Technology Using this strip I've figured that I'll be saving over $18 a year in electricity. The strip costs $26.41 at Amazon so you can recoup your investment in about 16 months.
The strip is designed so that if one 'control' device is off then other outlets on the strip will have no power. This is a good way to automatically power off for accessory devices like the printer and monitor on your computer or the DVD player and cable box for your television. So for example when my computer is powered on the outlets for the printer and monitor will have power but when the computer is turned off those outlets will be unpowered.
The key benefit of the power strip is that it keeps your unused electronic devices from leeching power even while they are turned off. Many of our electronic devices have standby modes and while they are turned off they can draw anything from a fraction of a Watt up to 5 or 10 Watts. thats power that is always on and always costing us money.
I measured the usage of the devices with a power monitor device. I got this one: P3 International Kill-a-Watt electricity usage monitor. It plugs into your AC outlet and then you plug the device you want to measure into the monitor. It has output display for voltage, watts used, amps used and a meter to measure total killowatts/hour used. So you can plug a device in and easily see how much wattage the device uses. Or you can plug a device in long term and see how much power in terms if kW/hr it uses. Its great for figuring your electricity usage and costs per device in your home.
With the kill-a-watt monitor I measured the power consumption of my computer peripherals. I have 2 printers and 2 monitors setup. The printers use 2-3 watts each. My older CRT monitor used 4 watts and the new LCD monitor used just a fraction of a watt. I also have a 19" CRT television and DVD/VCR player setup near my computer that I sometimes use to watch TV while I'm using the computer. The 19" TV uses 8 watts while off. The DVD/VCR seemed to use a fraction of a watt. After measuring all my devices I picked the items that used the most power and connected them with the smart strip. In total the devices used about 21 Watts total.
I also checked the power consumption of the electronic devices setup in my living room and connected to my main TV. I have a big screen TV with a cable box DVR, Tivo, stereo amplifier, HD DVD player, DVD/VCR player and a Nintendo Wii. The cable box and Tivo have to remain on all the time in order to record shows unattended. The stereo amplifier and HD DVD only used a fraction of a watt each. The DVD/VCR used about 3 watts and the Wii only used 1 watt.
To figure my annual power savings per watt I figured 24 hrs /day * 365 days/year * $0.10 per kWh * 1/1000 kWh/hr = $0.876 / W So 21 W * $0.876 /W = $18.39
The exact amount of energy you will save will vary a lot and will depend on the specific appliances you are using.