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.
MapQuest offers a turn-by-turn navigation app that'll bark directions at you for free, but the maps are only top-down, not the street-level-view that you've come to know and envy. Skobbler offers that 3D street view, just like the big dogs, for the low low price of $0, by using OpenStreetMap's user-edited, license-free database of maps.
On the plus side: it's free. On the downside: you're relying on the cartographical wisdom of the masses, so things are far from perfect. In fact, one of the most prominent features is a "bugs" button that lets you report the specific way in which your OpenStreetMap led you astray. That's not exactly the resounding confidence I'm looking for in an app that's telling me where to go. Skobbler's also a little bit sluggish, and the design isn't nearly as polished as some of the pricier competitors.
But still, it's free, it only downloads the maps it needs (and thus doesn't take up much space), and, eventually, its success could shake up the pricing of the more polished turn-by-turn apps. If the price tags of the fancy schmancy nav apps made you think you'd never have street-level turn by turn directions on your iPhone—and if you have somewhere to go but are in no particular hurry—Skobbler's worth a look. [iTunes]