HOBO data loggers from Onset record temperature, light intensity, rainfall, wind speed, and other environmental conditions. The kilowatt-hour transducer is the most obviously practical: for $270-295, $299 for a data logger, and about $110 for a current transformer and pulse input adapter, you can track which of your home gadgets are pulling the most power. Once you discover that your plasma TV sucks juice like a preschooler with a Minute Maid addiction, you can save back the money this gizmo cost you.
Or you can grab a light and temperature pendant logger for $39 and IM your friends about the weather, as if you took a healthy stroll through the park this morning.
HOBO products have software for both major computer platforms, so Windows users can slap temperature logs into Excel, and Mac users can perform interpretive dance to barometric data.