If you're one of those folks anxiously waiting for Google to release a mobile version of the sky layer they've got in Google Earth, you're partially in luck, because there's a comparable service called Starry Night (Download.com listing) that's launching a mobile version today. While there have been various iterations of the app in desktop and widget form for a while now, today makers at Imaginova are serving up versions optimized for Blackberry phones and Apple's iPhone.
The app is dead simple to use: Just use your phone's arrow keys, (or the Blackberry's rolling ball) to maneuver around the virtual skyscape. You can also zoom in and out, which will separate some of the constellations and planets that are bunched together. To help you in your quest, you can set the time of day when you're viewing the sky, and where you are. The default location when you're starting out is Canada, but you can switch it either with a ZIP code or your latitude and longitude coordinates, which admittedly isn't easy unless you're using a GPS-enabled Blackberry like the Curve 8310 and 8830.
The one thing severely missing on the iPhone iteration is any kind of touch implementation. If you're a fan of the Google Maps application, Starry Night is nothing like this, and you're stuck with some fairly limited zoom and movement controls that make it difficult to traverse large distances quickly. It's also a little slow to load, even over Wi-Fi. I still really enjoy the idea of having an entire map of the sky in my pocket at all times, and it can make for some boredom-killing goodness the next time you're gaping up at the heavens.