There's no reason you can't stay warm and look great at the same time.
Since winter is inevitably cold, I typically forgo small, lightweight outfits. Sure, they are cute in the summer, but I like to take advantage of the winter weather to embrace the possibilities of cozy winter wear. There's no reason you can't stay warm and look great at the same time.
Patterned sweaters are always fun. My favorite has penguins on it and was originally purchased because I was researching Linux. I like designs that are artsy, creative and not too serious. Solid colours are great as well. This winter staple evokes someone in a Hallmark Christmas movie who wants to reconnect with their family.
The sweater dress is classic in deep colors like dark purple and forest green. These dresses have all the style of a party dress, plus the warmth needed for cold nights. They also go well with wool leggings and socks.
For a different take on 'formal,' I like button-down shirts, especially in dark blue and black. The long sleeves keep my arms warm and it's easy to put an insulating layer underneath. Sometimes I'll put a patterned vest on top for the 'pretentious, scholarly fantasy character' look.
Lastly, fun accessories are a must. I have a lot of scarves, gloves and necklaces in black, silver, gold, red, green and other festive colors. They aren't just for Christmas--I'll typically wear something like this for New Year's Eve, and all through the season leading up to the festivities as well.
Whatever your style, you're sure to find a great outfit in the world of winter fashion.