I'll add that this system is also worth looking at. It's what I purchased a couple of years ago, and had it installed at the same time we added a whole-house generator:
Sense Energy Monitor
I saw it on This Old House, and they've since done an update.
It's got a lot of neat features, including the ability to download the data. I was able to use that to see if demand-based electricity would be more economical for us (rate varies by time of day). But you could also use it to track how much power your theater uses (surprisingly low for us) and how much it costs to use halogen can lights ($$$).
It can also be integrated with certain energy plugs to track specific device usage.
The drawback is that it requires professional installation, unless you're very comfortable working behind the electrical panel and at your own risk (I wasn't).
Scott
