XROAD G-Map Navigation
Did a quick search and didn't see anything about this posted. I've been using this the last few days and it works well. The one thing about this program is that it installs the maps on your phone, so no cell signal is required to run it. Of course, that means you've got a good chunk of your memory taken up by this program, though.
It doesn't have voice, but it does do turn by turn directions with a heads up display instead of always north. It also has a 3D view to it. It is available in two separate apps, the US west and US east. They are $20 each in the App Store.
It's still not a Garmin replacement (to me), but it is a nice app. Sometimes it feels a little odd the way you go about entering the addresses, etc., but I think in time you will get more used to it.
Here's a link to their site if interested: G-Map_for_iPhone