There are topographical map apps that are handy, so that you can use your phone as a GPS unit in the outdoors. Obviously you don't want to rely on them entirely for navigation, but it's a nice supplement to the map and compass, and a lot cheaper than buying a dedicated GPS unit.

Other than that, Google maps does everything I want it to do, with the one exception that I can't pin arbitrary locations. I really want to be able to pin locations, the best I can do is send the location to someone else, but I can't just save it on my phone.