Keep warm in style with the latest celebrity topper—a knit beret. Stylist Mariel Haenn likes Rihanna's laidback look because "the knit hat is a great contrast with the bustier to keep the look casual and cutting edge." The style is best for those with a bob like Rihanna's or Cameron Diaz's long layers. Says Haenn, "It definitely helps to have hair framing the face, so it feels as though you are using the hat as an accessory rather than a cover-up."

—Betony Toht