The amount of your bill doesn't indicate that power consumption of all these devices...power companies' rates vary a lot from place to place. But you are right in saying that heating and cooling devices require the most amount of power to operate, and are representative of the majority of your electric bill. Even a few degrees makes a difference...you can save even more money by getting a high-quality thermostat which will regulate temps more accurately.
-= SsZERO =-
<< I have a one bedroom apartment that my fiancee and I share. We have in this place 2 pc's (same as listed rig), and xbox, ps2, gamecube, psx, dreamcast, saturn, nes, snes, genesis, 2 vcr's, 5 disc dvd player, tivo, 27" sony vega, 25" sanyo tv, 600w receiver, 5 disc cd player, full size stereo system, a gazillion fans, many more electrics, AND an AC that keeps my hiz-ot azz near 70ish! My most expensive bill last year was $136. I turned my PC's off last year for a month solid and my power bill ROSE. We attributed it to the lowering of the AC by a whole two degree's.
What does that mean? I leave my PC on 24/7 and just kill the monitor. Tell yer friends to raise the AC if they're pissy about the powerbill >>