Personally found all of Lord Denning's books really interesting (he has 5 or 6) and I mentioned 1 or 2 in my PS. Lord Bingham - The Rule of Law is a pretty interesting book, as is either of H.L.A Hart's or Jeremy Bentham's books. All have a variety of interesting discussion points, but if you want this part of your PS to stand out don't go for something quite common that you think looks good, talk about something that genuinely interests you or leaves you curious.