[Editor's note: Not for the faint of hear, but great proof of concept of what the iPhone is capable of.]
xGPS uses Google’s map data and driving directions, adding a real-time navigation readout and a voice engine. You can also select a map area to download ahead of time, just in case you expect to lose your data connection during the drive. As you can see in ModMyi‘s video above, the app also supports a number of external GPS units, so 1st-gen iPhone and iPod Touch users can get in on the monotone fun too.
The project has been gestating for a few months now, but many vital features, including the voice engine, weren’t implemented until this release. xGPS 1.2 is now will soon be available in Cydia. UPDATE: An older version without vocalization in current available in the repositories, but the newest version is expected to be publicly available within the week. [xGPS via ModMyi—Thanks, Aleksey!]