I've just acquired a kill-a-watt power consumption meter. It's a pretty nifty gadget and with it I've been able to roughly calculate how much some common devices cost to power up. For example:

A Dell M5200 laser printer uses 960 watts while printing, so if you printed continuously for 24 hours, you'd burn up $2.46 worth of power.

My laptop uses 80 watts while active, so if I leave it turned on and running for a whole day, then I've spent $0.20.

A 100 watt light bulb burns through $0.26 per day, while a small desk fan requires $0.08 and a cell phone charger $0.01.

These costs are based on my residential electric bill. Here in the Allentown, PA area our utility is PPL and rates are structured so that you pay one rate for the first 200 KWH consumed, a slightly lower rate for the next 600 KWH and a third, even lower rate for additional KWH. The max rate comes out to something like 0.11/KWH although this is scheduled to drastically increase in 2010.