Now, I mainly use free Google Maps and Google Navigation on my Droid X, but CoPilot Live is a nice low-cost option (only $4.99).
Here's a snippet from their press release:
Already a popular choice for iPhone and iPad owners, CoPilot Live USA for Android provides easy to follow, powerful turn-by-turn guidance with clear 3D guidance views and voice directions throughout the USA. Detailed street-level maps are stored directly on the Android device, not downloaded each trip, so drivers don’t need to rely on a mobile internet connection for navigation.Learn more here: http://www.alk.eu.com/
Destination entry is made easy thanks to predictive address matching that finds addresses as you type. Millions of useful Points of Interest (POIs) are pre-installed as standard, including gas stations, restaurants and attractions. The app also features sophisticated guidance features such as ClearTurn™ realistic display with lane indicator arrows and real sign post information for clear guidance at highway exits and complex intersections.