My suggestions come from observing the plants at the top of cadalac mt. on Mt. Desert Is. in Maine. (suspect wrong spelling)and from other places. I have noticed native lowbush blueberry, Vaccinium angustifolium, Wine-leaved cinquefoil, Potentilla tridentata (I think), native ground hugging Juniper and the seaside rose, Rosa rugosa. Another plant that seems to thrive in windy, sunny places, but may not form a dependable solid cover, has the common name 'Thrift'. Armeria maritima, I think. Only the juniper and blueberry can tolerate some shade.