Smaug has a very small role in The Hobbit: An Unexpected Journey. The latest TV promo for the film features a couple of shots that seem to show him attacking Dale, part of his rampage that saw the Dwarf kingdom destroyed.
Here is that video, and below, some screen captures. It's a teasing glimpse, so don't expect too much. And remember that it could be a long while after December 13th we actually get to see anything better than this.
In case you're a human and blink, here are some frames from Smaug's flight.