Mary Bilder mentioned that there are some other antebellum law school buildings--beyond Princeton Law School's--that have survived into the twentieth century. She mentioned Litchfield Law School's building in particular.
Thanks to the Library of Congress' website on the Historic Building Survey, here's a New Deal-era picture of Litchfield. I have to say it's a rather different building from Ivy Hall (but then again it's a couple decades older).
Next up? Well, maybe I'll be able to scare up a picture of Lumpkin Law School in Athens, Georgia--though I seem to recall that it might have met in a building that's no longer in existence. I'll be on the case, anyway. Other possibilities--Winchester Law School; the University of Virginia and William and Mary, of course; Timothy Walker's Cincinnati Law School; Transylvania.... The possibilities are, even if not endless, at least great.