While there is no lack of classic sweaters, one of my favorites is still the Guernsey (named for, and coming from, the Bailiwick of Guernsey, one of the English Channel Islands). This sweater was introduced to me by a friend who grew up on Herm, another of the Channel Islands.
Some of the great features include a very tight weave (five ply yarn), distinctive shoulder stitching, and side vents. It is a long sweater. The length combined with the densely woven wool is formidable against the cold winds off the ocean. And there is no front or back designation, to even out the wear and tear.
This is a unisex item. Back in the 80's one of our friends was regularly seen in one of his many Guernsey sweaters with khaki shorts on those chilly summer mornings on the Maine coast.
Our most recent Guernsey sweater came from The Royal Male.