I bought my copy of Markides' book at Borders. I don't think it should be hard to find in a good "secular" bookstore.
Tom, I've heard good things about The Way to Nicaea and would like to read it at some point as well. I only made my suggestions because those are books that I have, unlike the others that were mentioned before my post, for which I'd have to do some hunting. If we can decide on a book to start out with, and it is something I don't have, if the seminary bookstore has it and I can make it there during regular hours to buy it, I'd be cool with that. It'd have to wait a little while, though, unless they are open the Friday after Thanksgiving, which I doubt.