iPhone MapOut is superb for planning routes, importing and exporting GPX files and for navigating with offline maps. Unique 3D terrain view to preview mountainous areas.
Scenic App is possibly one of the very best for iPhone. Free download and all basic features are free such as planning a route, navigating the route, etc, but you need to purchase credits for the premium features such as voice guidance, import/export GPX, etc.
Easytrails GPS is also very good. Various map options, import/export, navigate, but not for planning a route.