Google Flu Trends uses Google searches to find out where the flu is spreading. It only works in the USA right now, but hopefully it can be spread elsewhere (so to speak).

From the New York Times (stupid login information needed):

“What if Google knew before anyone else that a fast-spreading flu outbreak was putting you at heightened risk of getting sick? And what if it could alert you, your doctor and your local public health officials before the muscle aches and chills kicked in? That, in essence, is the promise of Google Flu Trends, a new Web tool… unveiled on Tuesday, right at the start of flu season in the US. Google Flu Trends is based on the simple idea that people who are feeling sick will tend to turn to the Web for information, typing things like ‘flu symptoms; or ‘muscle aches’ into Google. The service tracks such queries and charts their ebb and flow, broken down by regions and states.”