With bike shops, the deals come in the fall. That's when the past year's models are sold on clearance for space for the next year's models. For example, I think the new Cannondales have been coming for the past few weeks.
Before Christmas, the prices probably won't go down as much as the clearance sales that are going on around now. After Christmas, you might get something better.
With used bikes on craigslist and ebay, bikes may sell for lower prices during the winter, but you also have a smaller selection (People aren't thinking as much about selling bikes then).