Yep MotionX here too. Great app. You can load huge areas of OpenStreetMap or OpenCycleMap onto it so it doesn't need a phone signal in the field, and/or it can be online and use either Google or Bing maps.
Actual route navigation is done on a way-out system and works well.
Also with the new OS update it now runs in the background and continues recording your track while you do other stuff.
There is a free Lite version which is fully functional so try that.
I believe there are quite a few other contenders like MemoryMap that offer real OS maps, but they obviously cost a bit more.