Ones I have tried for iPad include National Geographic World Atlas and the four ScenicMag apps for the US. None are all that good. National Geographics gives you some detail for every country but needs a WiFi connection to give you really good detail (via Bing). The ScenicMap apps are good but very slow usually. I have tried tracking our progress while flying commercial and got it to work OK once but it is far from consistant and not the best UI. They need work. I also have TomTom and Navigon on my iPad but they are not all that easy to use as purely maps. I also have a Garmin nuvi and that works OK even when flying commercial but still not real user friendly as purely a map.

There is definitely a need for great off-line maps.