I can't remember how I managed to find this, but I first used it on my iPad and it was free for the iPad version:
https://itunes.apple.com/us/app/gosk...364209241?mt=8
It
Developer website:
http://www.gosoftworks.com/GoSkyWatch/GoSkyWatch.html
Most useful I find is the catalogue that you can sort by magnitude, and has wikipedia links to each of the objects. Makes planning out my viewing sessions quick and easy. The graphics are beautiful but functional.
I haven't explored that many astronomy apps but so far the people I've recommended it to love it.
