The other day, I managed to get hold of a CurrentCost energy monitor. Now, the nice thing about this particular monitor (apart from the ton of information on-screen) is the fact that it has a serial output on the bottom, which you can (with a bit of hacking) plug into your PC, and - bingo - lovely XML data!
However, once you have it connected and spewing XML at you, you really need something to do with all that data. I don't have anything big written yet, but my first step towards making something useful is a Ruby gem, which is available from GitHub. So far it can only parse the XML data from the meter - direct access to the serial port is hopefully coming soon.
In other news, the AMEE gem I started a while ago is still coming on. It can now use the XML and JSON interfaces, parse the whole Data API, and retrieve a list of Profiles. Not a bad start.