If you travel a lot, Triposo (free, universal) is a great addition to your app arsenal. Triposo has guides for pretty much everywhere, even out-of-the-way places for US travelers like Afghanistan, Chad, Latvia and Zambia to name just a few. In addition to country guides, there are city guides for most of the bigger cities around the world.
The app is basically a shell for region-specific data you download while planning your trip. Once it is downloaded, you don't need an online connection to use it.
The guide gives you an overview of the destination, along with detailed maps of its largest cities. The app includes a currency converter, weather and some useful phrases. In big cities, you get restaurant guides and suggestions for nighttime entertainment.
I downloaded the Arizona info. It was 50 megabytes, and reasonably complete, with lots of suggestions for outdoor activities. There was usually a brief description of the location, and often some info culled from Wikipedia. The only city with great detail was Phoenix, but the app showed hundreds of places to go all around the state. As you venture outside the large cities, the maps lose detail.
Triposo is a really useful app, and a nice partner to the Crash City Guides that I looked at a few days ago. The only negative I found for Triposo is that while the app will show your destination on a map, there are no directions to get there. A lot of apps will link to Google or Apple Maps, making navigation easy. That's a pretty significant weakness of Triposo, and one I hope to see fixed soon.
Having said that, Triposo can get you information on just about anywhere in the world, and that makes it unique for something you can carry in your pocket. If you travel, you're sure to find it valuable, and I recommend it.
Triposo is a universal app and is optimized for the iPhone 5. It requires iOS 5 or greater.