Hollywood stars have been warming their toes in Uggs (uggaustralia.com) for years, but if you want to diverge from the ubiquitous Aussie icon try Khombu. A shockingly warm boot for its minimalist look is the Carol ($150; khombu.com). The tall, flat-heeled, waterproof riding boot with a neoprene-and-leather upper is rated to -20 thanks to its breathable, moisture-wicking, shock-absorbing Thermolite fleece lining. Don't be surprised if you see Lindsey Vonn kicking around in Khombus—the company sponsors the U.S. Ski Team.
I also like the Spanish company El Naturalista. Their boots come with a Euro look, intricate construction, and the company's "Ten Commandments"—a public commitment to fair labor. The Inuit ($230; elnaturalista.com), an ankle-length, full-grain leather bootie has a grippy recycled rubber outsole that will keep your girlfriend upright on the ice. The fur lining adds glamour, but it's not faux.
For warmth, you can't go wrong with Sorel's classic 70s-era Caribou. For fashion, try the mid-calf, lace-up Cate the Great ($200; sorel.com). With a faux-fur collar and a warm felt liner, the Cate is rated to -25—perfect for walking through a snowstorm to your favorite Chicago bar. Plus, Sorel's signature replaceable felt liners ensure your Sorel will be around as long as your girlfriend is.