Whenever I am in Seattle (far from where I live) I visit this shop. If you go to a bookstore, even a good one like Eliot's, further down 1st Ave, your choices are limited to the current crop of books, most of which are not good enough to survive the decade. Wessel & Lieberman has the books good enough to survive the decades, of all kinds. Collectibles, but not just that.
Pros: short walk from Pioneer Square.