Google Maps Navigation is a wonderful turn-by-turn navigation app for Android. Only problem? It's only available in the US and UK. Thankfully, Skobbler is bringing their own free turn-by-turn navigation to the rest of the world.
The TomToms and Navigons of the world have street-level turn-by-turn navigation down pat, but they're expensive. Skobbler uses OpenStreetMap, the "wikipedia of maps," to deliver its turn-by-turn directions for free, but it's kinda a "get what you pay for" thing.