The comet ISON is currently barreling toward the sun with a close solar encounter due on November 28. It's currently visible in our morning skies, but will become a night-time sight in a few months if it survives the close approach to the sun.
Comets are notoriously unreliable. When Halley's comet returned in 1986 it was pretty much a bust for visual observers. ISON could shine as brightly as the full moon, be a dim asterisk or something in between.
That brings me to the the Comet ISON app (US$0.99). It's the nicest comet-finding app I've seen so far. It will help you locate ISON, then let you get aboard the comet for a 3D fly-through as it heads toward the sun and beyond.
In addition to the beautifully rendered 3D views, there is ample information on the history of comets, with animations and other videos. The app also lets you share your view of the comet with others.