The first I downloaded was GoSkywatch Planetarium
A fantastic app that makes the iPad a magical telescope that when pointed towards the sky it maps all the heavenly bodies up there!
The second is from the same company, but is a seperate standalone app, it works in exactly the same way but it tracks satellites, space stations and other mechanical space vehicles, very interesting......if you like that sort of thing
I've been using the first for a good while now, and use it regularly, perfect for the beginner, amateur and even the experienced astronomer, the second is just a great way to find what those slow moving bright lights are in the sky.
Treat yourself to an early Christmas present, whilst led on your back out on the street, looking up to the sky dribbling and making that annual promise not to drink again, you will be able to name every star and satellite looking down at you.