Astromo
Astromo is a utility that combines the Armillary and Orrery widgets and adds an extra set of detailed ephemeris information.
Orrery
The Orrery mode allows you to see the current location of the Sun, Moon and planets, as well as telling sun rise/set times (including various twilight times) and moon rise/set times. Dragging the Sun will move it through the day, while dragging the zodiac ring will move between days.
Armillary
The Armillary mode gives you a view of the current overhead sky, with various celestial coordinate lines, constellations, and other heavenly bodies. You can zoom in (with a double tap) to get a better view in one direction - twist (using two fingers) to rotate that view.
Ephemeris
The Ephemeris mode shows detailed information about exact locations (in all major coordinate systems) of the various heavenly bodies, as well as times of rise/set/transit and other interesting information.
Astromo further uses the current location of your iPhone/iPod Touch, so automatically updates regardless of your location. All three modes also allow you to change the time or date (or switch back to the current date/time).