Mapper is an iPhone application I made to use while I'm driving. I was originally using the native iPhone map, but I got tired of constantly having to find my location repeatedly.
Mapper automatically locks on to your location as you move. It also scans your address book and adds every contact with an address. If that contact has a phone number, that too is displayed on the pin's pop-up box. Clicking on a pin (like in the picture) and clicking call will call that person. Clicking message will record your voice and translate it into text for use in a text message (currently under construction, which is what the play button is for). I've also extended the status bar, adding speed, current city, and temperature. There's also a button that marks your parking spot, which can be useful.
Check for it in the app store in a few months when I get all the features completed.