iSkyGaze tells you where to find various objects in the sky, depending on your location and the time of day. Sure, it'll show you where to look to see the sun and moon, but iSkyGaze also helps you spot things in deep space, like the Orion Nebula. This cool app even tells you how far away the object is, and the best time to see it.
Want to know how the sky looked on any given date from the past 10 years? Starry Night Mobile will tell you. It can also predict what your overhead view will be 10 years into the future. Just enter a zip code, landmark, or address and let the app do the calculating for you.
If checking out satellites or the International Space Station as it passes overhead is more your thing, then you'll love LookUp. Once you enter your location, the app will tell the precise time various orbiting objects will zoom by, complete with exact elevation stats and how much time you'll have to see it before it dips below the horizon.
Oh, and here's a bonus app for all you werewolves.