Lower brightness levels, make use of power stepping/limiting, have them off at all possible times, turn off the monitor at least. Unplug expansion cards/devices when not in use.
What can also help with power is room lighting. I have 160watts in my ceiling fan, but during the day time opening the window is just as bright. At night, all that power is WAY too much. So I unplugged 3 of the 4 bulbs, and a 40watt bulb is more than enugh for lighting purposes in my room.
Invest in dark screens for the windows in your house. They stop heat from getting in but allow light in, kind of like a 1 way mirror. You save on AC costs and keep your room much cooler during the hot day.