First, the most professional is the "shirred shoulder turtleneck" (pictured right in the sky blue). It features ribbed cuffs and hem, and slight sheering at the shoulders. Made from rayon and nylon. In addition to the blue, it comes in four other colors, including the office-standard brown and black. $44.50; find it here.
Second, still on the professional side is the "rib detail turtleneck" (pictured left in the garnet red). It features similar ribbed trim on the cuffs and hem, though a bit finer, and a wide-ribbed trim around the shoulders and turtleneck. Made from rayon and nylon also. In addition to the garnet red, it comes in four other colors, including a lovely deep purple, and, of course, black. $44.50; find it here.
Finally, on the less professional side, better for more casual days, are the "striped turtleneck" and "tiny stripe turtleneck." The tiny striped turtleneck is pictured right in the green. The striped turtleneck features wider stripes and comes in a garnet/grey combo and a black/grey combo. Both are made from rayon and nylon. And both are $49.50; find the striped turtleneck here and the tiny stripe turtleneck here.