Are you wanting to navigate or just record your route so you can look at it on a map later?
For the former I use ViewRanger
For the latter I use Endomondo
ViewRanger is pretty good when you want to plan a route on a PC/iPad then upload it to your iPhone to follow when you are out and about. You can pre-download all the map tiles while you are still on wifi so you don't need a 3G signal while you are "in the field". You can also set it to alert you when you stray too far from the route you are following.
Endomondo is pretty good if you just want to record your travels then take a look at them later on the website. It will display the route you took on a nice big map along with distance/speed/height etc