the power your GPUs are eating is pretty much fixed, unless you underclock the GPU, but your hash rate will drop, and you don't want to save power that way. Here's what I did:
-UNDER clock and UNDER volt your CPU, there is a lot of idle power wasted on older, pre-CORE CPUs
-Boot off of a usb drive, so no spinning HDD is required.
-disable onboard devices (raid controllers, audio chipsets etc) in the bios
-Down clock the video memory, this hasn't show much power savings, but may reduce heat.
-Use only 1 stick if ram
-Remove all non essential peripherals, floppys, dvd-rom drives, soundcards
-Remember to physically power off your monitors, as they still consume power in standby
Even after all this, I saved maybe 30w out of 1000