Kayak.com have created a Google Map mashup that will do a live search for cheap flights from any airport in the world.
To initiate the map the user just has to type the name of an airport in the search box and press 'change home airport'. The map then shows live searches for cheap fares to other airports around the world. Each flight path and airport is then added individually to the map.
Clicking on any of the map markers will open an information window with details of the fares and a link to the relevant page on Kayak.com. The fares are also displayed underneath the map.