The International Association of Book Towns ("a small rural town or village in which second-hand and antiquarian bookshops are concentrated") collects information about delightful bibliophiles' paradises. I once spent a magical day combing the shops of one of these places and by the end of it I was drunk on binder's glue, ink, and silverfish.
I.O.B. – International Organisation of Book Towns
(Thanks, Marilyn!)