Since no one else has responded I'll toss in my two cents:
For it's price ($2.99), it's intuitive user interface and feature set I like MotionX GPS.
I wasn't going to mention it on this thread because in normal use, you have to have a data connection to AT&T to get the map of your current location. However, you can pre download maps of your route before you go so you will already have them in memory. Once done, you can access all the maps of the area you've downloaded without any cell phone connection at all.
The down sides are that...
* you have to take the time to download you route (best done in sections) and it takes a long time.
* if you only want detailed maps for a 100 mile route you still need 50 to 100 MB of data.
* if you need to do a full reset on your phone, you could loose all the maps you so laboriously downloaded, until you restore them from the automatic backup on your PC.
However, for $2.99 it is a great backup to a dedicated GPS unit.