[StarsandSky]

I have tried quite a few of those astronomy apps and like Star Walk the best also with Digital Compass that activates the ''Star Spotter'' function and follows your movements once pointed at the sky. It works in an excellent way, very smooth, the graphic is superb and lots of info included.
It is also the official product of IYA2009 (International Year of Astronomy 2009) and I can see why they chose it!!