Thuja occidentalis 'Degroot's Spire' (American Arborvitae)
One of the narrowest of the arborvitaes out there - and it's been out there a long time. Will grow to about 15' or so with the classic, flat sprays of evergreen foliage. Widely adaptable and easy to grow. An excellent hedger, specimen plant or in an loose, informal grouping.