I'm currently in Portland, OR and spent several hours yesterday in Powell's Books. It bills itself as "the largest independent used and new bookstore in the world," and it's easy to see why. It takes up an entire city block and is reminiscent of the large bookstores along Shaftsbury Avenue in London. You know, the ones that have acres of books from top to bottom that go on for rooms and rooms. I overheard a wife yesterday say to her husband, "Let's stick together. I've worried if we get separated that we'll never find each other again."
The selection is impressive. For example, Powell's has an entire bookcase, top to bottom, devoted to "Military Aviation." You'd be hard pressed to even find a bookshelf so labeled in a Barnes & Noble or a Borders bookstore. Definitely worth a visit if you love to read and are in the Portland area.