Some other apps I regularly use that haven't been listed:
The Photographer's Ephemeris - While designed for the photographer, it is useful if you want to position your RV with regards to the sun or moon (for the view, solar, etc) For any location and date it shows where and when the sun and moon will rise & set.
AccuWeather - Similar to Weather Underground
CardStar - copies your store discount cards so you don't have to carry them - they can be scanned from the phone.
Night Sky - A Star map
SPLnFFT - A sound pressure meter
Public Radio - links to most public radio stations
Pandora - on-line music
MotionX-GPS - A good hand held GPS app for hiking
iBird Plus - While expensive, this app is the equivalent of a good bird id book, complete with the sounds of each bird.
Clinometer - This is the leveling app I use the most.
All these are iOS apps, although most of them are also available for Android.