Back in February of 2008 both Aulus and I suggested Mary Beard as a possible guest. She is a classicist at Cambridge and well-versed in both Greece and Rome. Her latest book was about everyday life in Pompeii and the one before that was about the Parthenon. (Actually, her latest book is a compilation from her blog -- I'm on page 247! -- but I was talking in terms of books directly related to the classics.) We could discuss those things or perhaps classics in general and their place in the modern world. Bonus: She has a rather popular blog at the Times and we might get a little publicity out of it. I don't know if the contact info here is accurate or not, but I can't find anything at the blog.