My friend was in town for the weekend, and we traveled to Second Story Books. I'd been there before, but not in many years.
Second Story Books almost feels more like a warehouse than a bookstore. This feeling was exacerbated as, while we were there, a loading dock at the front of the store was open, letting in air. This was more than an aesthetic choice, as we found ourselves (and other customers) continually sneezing in the midst of the rather musty collection. Mustiness aside, however, the selection was quite impressive and reasonably well organized. I did come across a few grab-bag boxes in the sci-fi section, but they rather added to the sense of adventure and exploration that often accompanies used bookstores (for me, at least). In addition to generous fiction selections, Second Story Books really shined in the non-fiction, references, and antiques sections. Unfortunately, the latter means many of their wares are more expensive than in your average used bookstore, but extra interesting to browse!
While I felt a bit guilty for the three books I picked up, my friend's stack quite dwarfed mine. I asked if I might share her bounty with you as an example of the many obscure gems that might be available (though her selections are mostly representative of the Psychology and Human Sexuality sections). Her books are as follows:
My more meager selections included The Tolkien Reader by J.R.R. Tolkien, Babylon Revisited and Other Stories by F. Scott Fitzgerald, and The Princes in the Tower by Alison Weir.