I'm not too sure about "Northern Preppy", but where I'm from we've got our own breed of it: "Cape Cod Preppy".
Lots of the normal stuff - Abercrombie, A&E ( we tend to go the beachy/preppy look ), Lacoste. Then there's my favorite Vineyard Vines.
which if you don't know, you should all check out.
http://www.vineyardvines.com