Map my Run and Map my Walk.
That's my current fave. You can also do endomondo which will allow you to join challenges or even the Nike+ app. I like Map my walk because I can re-do the last walk I did and sort of challenge myself. Also, I notice the GPS is spot on, not that I had issues with Endomondo. I never looked into Map my run/walk, but Endomondo has a great site as well. I like both apps really.