If all you want is graphing, then Google Power Meter is probably the best way.
That may be an option if you are not concerned with accuracy. Also it is not available in every area. In my experience (you can see chart for last month at: http://yfrog.com/mvmx1g ), Google Power Meter is off by more than 20%, skips monitoring for entire days and only shows whole house data which doesn't really help you find less obvious "power hogs." We use EcoDog FIDO which shows data for each individual circuit and was accurate with our utility bill within 1KWHr for the month. It also shows the actual cost of the electricity & even accounts for our tiered rates & warns when we're approaching the next higher rate tier. Our utility has been saying that "Google Power Meter has a few bugs to work out..." for about 7 months now. EcoDog showed us that our old dehumidifier in the basement (that we completely forgot about) was costing $90/mo to run. We replaced the dehumidifier with an Energy Star model that paid for itself in 2 months. Unfortunately, EcoDog is quite a bit more than you are looking to spend & we've been running it in VMware on the Mac. They're supposed to come out with a Mac native model next year. It's pretty cool & we figure that we have saved enough electricity to pay for the EcoDog over about a year.
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If all you want is graphing, then Google Power Meter is probably the best way.
That may be an option if you are not concerned with accuracy. Also it is not available in every area. In my experience (you can see chart for last month at: http://yfrog.com/mvmx1g ), Google Power Meter is off by more than 20%, skips monitoring for entire days and only shows whole house data which doesn't really help you find less obvious "power hogs." We use EcoDog FIDO which shows data for each individual circuit and was accurate with our utility bill within 1KWHr for the month. It also shows the actual cost of the electricity & even accounts for our tiered rates & warns when we're approaching the next higher rate tier. Our utility has been saying that "Google Power Meter has a few bugs to work out..." for about 7 months now. EcoDog showed us that our old dehumidifier in the basement (that we completely forgot about) was costing $90/mo to run. We replaced the dehumidifier with an Energy Star model that paid for itself in 2 months. Unfortunately, EcoDog is quite a bit more than you are looking to spend & we've been running it in VMware on the Mac. They're supposed to come out with a Mac native model next year. It's pretty cool & we figure that we have saved enough electricity to pay for the EcoDog over about a year.