Nabeel Azar has created GeoIndex which mashes up Google Maps, Yahoo! Finance, and the S&P 500 US Equity Index. The mashup's blog notes that "..You could call this GeoCashing if you wanted to be punny about it!"
Mashup Description: On this map, the weekly returns of the S&P 500 constituent companies are indicated by an up or down arrow. The arrows are located at the center of the city in which each company is headquartered. Clicking on the arrows gives you a bit of company info and a link to that company's Yahoo! Finance entry.
There are more details on the map as well as how it was made here.