Google Maps, the new version, and the "new My Maps" app (by Nelson Kwan, $2 I think) to view the custom maps on my iPhone.
I used Nelson's old My Maps app, which I think I got for free, with the old Google Maps and was very happy with it, so it was easy to pay $2 for the new version, since he keeps it maintained. (e.g. I think Google changed the login routine that he goes through and there was an update to the app the day after I noticed it was a problem.)