Our API directory now includes 82 address APIs. The newest is the 1Map API. The most popular, in terms of mashups, is the geocoder API. We list 41 geocoder mashups. Below you'll find some more stats from the directory, including the entire list of address APIs.
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.