Librairie La Hune, Paris, France
I thought La Hune looked new when I first visited in 1990, but it was designed in 1949. It's still completely fresh: modern, urban, and precise. Steel and glass. There are no armchairs in French bookstores; one gets the sense that the layout is more for the books' comfort than for yours (Le Corbusier would probably have thought this appropriate). And yet it inspires a comforting thought: these books are so important that we should consider ourselves as guests in their space, not the other way around.
Montague Bookmill, Montague, Massachusetts
The Bookmill is warm, rural, and messy, like the attic of your aunt's country house. I love the rambling and friendly atmosphere. It's the comfort food of bookstores. This is a place where serendipity is the organizing principle; you always find what you weren't looking for among the used books. There are also two great restaurants and a good used CD store on the site -- and a beautiful waterfall! Their motto: "Books you don't need in a place you can't find."
Hennessey + Ingalls, Santa Monica, California
A modernist hangar that is a bookstore that feels like a museum. It's hard to believe that one can get lost inside a specialty bookstore -- the specialty in this case being art and architecture -- where every title deserves attention. There are few occasions today when we perceive the sheer physicality of so many beautiful books in one place. You can smell the ink used in four-color printing. Online, you simply don't feel the stacks as weighty and real. This place puts you in a universe of books. Or paradise.