So now it's kind of an obsession and I'm eager to find the next great book. The search is fun and I like making him happy!
Recently I was very excited to show him that I found Machiavelli's The Prince. He was proud of me and thankful, but he was also amused to point out that I had already found him The Prince and forgotten about it. Swing and a miss.
A couple months later I made up for it when I got Plato's Republic, The Iliad, The Odyssey, a book about Scottish Witchcraft, and a useful and well organized grammar reference book at a library book sale.
The next thing he has on his wishlist is The Malleus Maleficarum.