The Geminid meteor shower is usually one of the best of the year. Though the shower's peak is brief, on the night of December 13th and 14th, up to 120 meteors per hour are predicted, if viewers live in an area with dark skies. People will see some meteors before and after the peak days, too.
If you have a dark sky, you'll also see the winter Milky Way rising between Orion and Gemini, bisecting the sky. The constellations Perseus and Cassiopeia are nearly overhead and are easy to see, even from the city.
If you haven't tried to find the asteroids Ceres and Vesta yet, they're at their best this month, too. And they're easy to find near Jupiter. All three objects reach opposition in December, when they're best for viewing.
Mercury, Venus and Saturn line up in the predawn sky from the 9th through the 21st. Finally, on December 25th, watch Jupiter next to the moon an hour past sunset.