New Trail Maps app for iPhone and iPad by National Geographic [Smartphone Apps]

I haven't had a lot of time to play with it, but you iPhone users out there might want to check out "Trail Maps" for iOS. It allows you to access USGS topo maps for the whole US, and you can download maps for a specific area before a trip, if you know or suspect that you will be without data (or are on a limited data plan).

I'll post a more detailed review soon, but here are a few screenshots that will give some idea of the apps capabilities.

UPDATE: After using the app a little bit in the field, I've got some comments.  I like the fact that you can download maps for offline use.  This was very easy to do, and worked pretty well over a 3G connection (not reccommended on a limited data plan, however).  The resolution of the maps left a little to be desired, however.  Whenever I zoomed in to get a real detailed view of an area (to a scale of 1 inch = .25 miles or less), the app would switch to the Bing aerial map.  So while this app is pretty useful from a big picture perspective I don't see it being useful for following the intricate twists and turns of a porrly marked trail.  I wish there were a setting to let you zoom in beyond this seemingly arbitrary limit.

That said, for 3 dollars, I think this app provides a lot of functionality. That 3 dollars also gets you the iPad version which is scaled to make use of the iPad's screen.  So, especially if you have an iPad, I think this app is worth adding to your digital tool kit.