http://www.greeneyemonitor.com/

http://www.brultech.com/store/

This lets you monitor (in real time) the true power in every power circuit in your home, plus one-wire temperature probes, plus 4 pulse monitors (for monitoring water or gas usage), and can integrate with home automation systems (zwave, insteon, etc), and all for less than $500.00.

First, it's amazing how you can lower your energy bill when you can accurately monitor your energy usage with such granular detail. It'll more than pay for itself. Also, if you want to do much home automation stuff, it greatly reduces the number of automation items you need to purchase.

I live in a 5000 sqft home in East Texas built pre WWII (and looked the part), and it's been invaluable in prioritizing energy efficiency upgrades. My average utility bill (we only have electric, no water or gas bill) was $600/mo when we moved in. It's now less than $150/mo. We don't have solar panels or anything else exotic and, haven't adopted any wild Eco-centered lifestyle. (For example, my house temp is usually between 68-70 in the summer and I'll set my bedroom to 65 at night)

Some quick examples of what I use it for --

I have a open loop geothermal heat pump for a 4 zone hvac, and by monitoring water and air temps, power usage, and water flow, I can keep track of the efficiency of the system and be notified of all sorts of things. Some useful, some just our of nerdy curiosity. For example, the fan on my hvac system has 5 speeds and there's no easy way to monitor what speed the fan is running at, but just by monitoring the system power, I now have a power signature where it's easy for me to know what speed the fan is running at. (I bought the unit as a "scratch and dent" unit and installed it myself -- total cost with all the plumbing, wiring, etc was about $7,000)

I monitor our water well pump run times, etc and get a text when my well tank needs an air charge adjustment to prevent pump over cycling.

I get a text when the washing machine and/or dryer is done. It doesn't matter if my washing machine is on the same circuit with a bunch of other powered items. Because I now know when the washing machine cycle ends the wattage on that circuit drops by 145 watts, so I have it set up to text me when the wattage drops more than 142 but less than 148. I can even tell exactly what mode the washing machine used--was it set to whites, heavy wash, delicate, etc. (not that I really monitor this, but based on the power signature, I could)

It's pretty crazy how much information you can pull out of real time energy monitoring, I can pretty much map out exactly what people did in my home throughout the day.