Astro Panel (Free - no IAP) is an app that displays detailed weather forecasts and lunar information for astronomers.
SkEye | Astronomy
This app (Free - no IAP) is for astronomers that can be attached to a telescope.
Google Sky Map
Google Sky Map [Free] is an app made to complement Google Earth. Essentially it is the same thing, but with stars, constellations, and planets.
The NASA App (Free - no IAP) is an information based application that can help astronomers be more aware of NASA's current activities, such as missions and the locations of s...