Power consumption
Call me a geek, but I like graphs. Here's a quick and irregularly measured history of my home power consumption.
It contains three data sets: average daily power usage (kWh), average daily temperature and annual average power usage. Temperature has a monthly granularity, power consumption is somewhat more irregularly measured, but close enough to monthly to be useful. As you can see, there's a rather strong connection between temprature and power consumption: I use (extremely annoying) electric heating. Hopefully with enough data this graph will show a bit of a downward trend in power consumption!
