Google Sky Map for Android turns your Android-powered mobile phone into a dynamic window on the night sky, and have access to a compass reading as well as the other sensors, and so they can also determine the direction you're facing. Once you have a phone with a compass ("magnetometer"), a plumbline ("accelerometer"), and you can pinpoint your position (using GPS) and your time (using a clock), that's enough to work out which direction you're pointing in the Universe. Point the phone at any part of the sky, and Sky Map gives you a specially constructed map telling you what stars, planets and constellations you're looking at. You can even search for stars and planets by name, and the phone displays an arrow telling you how to move to face the object you're interested in.
To try Sky Map, visit Android market, and search for "sky map", or you can find the application listed by popularity in the Applications > Reference section.
More info: Google Mobile blog