HP Photosmart C5280 All-In-One is printer, scanner and copy machine. It is pretty new and I expected it to be resource friendly. First I checked how much energy uses power supply alone, with no printer connected. It was 0.7W. Not bad.
When I connected printer, and after power draw stabilized, it used 4.8W of on standby (plugged, but powered off). That's pretty bad.
When it's powered on, energy consumpiton increases further to 5.9W on idle. Pretty much for modern device - it's better to leave it off when it's not used.