Josh Curtiss is creating an app that I think will help many business like door to door sales, marketing, parole officers, child welfare workers, law enforcment, etc.
Hound is an iOS app that allows you to add multiple people along with their address and easily find them on the map. It also gives you a map view of all your contacts to be able to visit folks in close proximity of where you are going.
App should be ready for app store soon. I will post link here when complete.