[Ogre]

I used this topographic map app for iOS while hiking the Appalachain Trail last year: http://itunes.apple.com/us/app/topo-maps/id306014271?mt=8

It's currently $7.99, and I felt like it was worth every penny. That $8 gets you unlimited downloads of USGS map squares, which are saved for offline use. Although the support for GPX "routes" is a little lacking, the support for "waypoints" is fine. My use case was mostly putting all of the AT shelters in as waypoints so I could answer the question "Oh my god how much farther do I have to go today?" when I took breaks. But it works very well for actual navigation too.

Also, the developer responded within a few hours when I was having trouble downloading a particular map square. It turned out to have more to do with my crappy Edge connection at the time, but still, he was quick to help, always a plus.

The big drawback to not having a dedicated device is battery life. I had to ration out use of my phone pretty strictly at times. Going 4 or more days between chargings doesn't actually let you do very much with it. If you only care about day hikes and overnights, it's not such a big deal, just remember to turn it off when not in use!