Killer map.

InfoWorld: "'...some of the key services that have been introduced that are really world-changing -- that in some previous model would have been recognized as the killer apps -- they're just Web sites,' [Tim] O'Reilly arched an eyebrow. 'And because they have an e-commerce model like Amazon or an advertising-based model like MapQuest, people don't think of them as software products. But MapQuest is just as revolutionary a killer app as the original spreadsheet.'"