You didn't say anything about air conditioning, which I've observed to be the single largest source of electrical draw in our house (two zones, each of which consumes ~2.5KW). All the usual advice about passive mods to your house (avoiding air leaks, reflective films on windows, light-colored roof, etc.) can add up, as can using an electric ceiling fan in lieu of dropping the temperature even further.

Your computer, of course, is a power hog, and I'd imagine that you don't need such a monster to be on 18 hours per day. My MacPro tower at home goes to sleep when I'm not using it, saving me its 150-200W power draw when idle (monitor off, disks asleep, CPU on).

And, if you've got lights that are on 24/7, consider getting a timer. I've got this solar timer model for our porch lights, which you program with your lat/long, and then it can do dusk-to-dawn or dusk-to-specific-time modes. You might also consider replacing tungsten bulbs with CFL or LED alternatives, which also have the benefit of putting out much less heat, and thus saving you money on the air conditioning it takes to remove all that heat you don't want in the first place.