When it comes to map mashups there's no doubt that Google Maps leads the way. On ProgrammableWeb we list 1,964 Google Maps mashups, almost four times as many as any other API. This popularity makes utilities built on top of Google Maps especially interesting, such as this contextual menu control, which pops up a menu when the user right clicks.
One of the bigger challenges with anything having to do with software-as-a-service (SaaS) applications is how quickly they can sprawl out of control. Before most organizations realize it they wind up with multiple silos of SaaS applications that are even more difficult to integrate than traditional enterprise applications.