turtleneck

Turtleneck

Great for: Women with long necks, small-to-medium-size busts, and anyone wanting to cover up wrinkles or skin imperfections.
scoopneck

Scoopneck or V-Neck

Great for: Almost everyone. They flash just enough skin and create a flattering visual line.
crewneck

Crewneck

Great for: The same women who look good in turtlenecks. (Not so great for: Anyone with a short neck or big bust; the style offers no elongation and overemphasizes curves.)
boatneck

Boatneck

Great for: Women with narrow shoulders, which look broader in this style. (An easy way to achieve an hourglass shape is to make your shoulders appear wider than your waist.)

More O style:
From the September 2010 issue of O, The Oprah Magazine