Earlier in the summer I purchased an FGM-3h fluxgate magnetometer and rigged it up to the Arduino and a database on the website. Finally I've got around to doing a proper page for it - so click here to see the live magnetometer data.

UK Live real-time magnetometer data

The page allows you select a date period for the data. The magnetometer data allows you to see the changes in the Earth's magnet field during the day caused by the diurnal cycle of the field and more random stuff caused by solar flares etc.