Walking down Lexington Avenue in the Upper East Side earlier today, I came across Archivia Books, a newish (open since November, 2007) bookstore specializing in architecture, art, design, decorative arts, gardens, interiors. While small in terms of square footage, the shop packs plenty of books, with a very good selection of architecture books along one wall.
The majority of architecture books are high-end, with the usual Phaidon and Taschen behemoths alongside various monographs, abundant regional titles (a lot focusing on Kentucky, for some reason), and a fair number of picture books of historical architecture, fitting the store's speciality. A few of the titles that caught my eye (below, l-r) were Contemporary Houses by Antonio Corcuera, Paradise Lost: Persia from Above by Georg Gerster, and New Prefab Architecture by Sergi Costa.
My NYC Bookstores list has been updated, with Archivia Books tied for 11th.