Consider the "Epidemic Watcher" idea. This could be easily implemented with the Google Maps API, tied to a medical news aggregator and partnered with WebMD. Now it may sound silly to watch a particularly nasty strain of the common cold march its way across the Midwest, but the idea becomes vastly more interesting when you start to plot SARS, Avian Flu, West Nile, etc.
Combine News articles and a graphical geological representation of an infections march and I think you might actually have a winner on your hands.
Although, the vast majority of the sites visitors may be hypochondriacs at least you have a good idea who to target your advertising to.