Google recently launched a beta version of Google Maps Navigation. As the name hints, it’s based on Google Maps but it’s also heavily updated with new stuff because of the “navigation”-part of the name.
At first, the software will only be available for Android 2.0 but it will be free and ad-sponsored. The advertisements are based on your location.
The navigation will include speak and turn-by-turn navigation. Google Street View should be available too in certain areas.
More information: Google Maps Navigation (beta).