Today, by coincidence, I visited Mainly Books, a second hand bookstore on Bulwer St in Highgate. I am going to do a proper post about this sometime in the near future, but I was so awesomed out by the rickety old shelves piling books to the ceiling, and overwhelmed by the books that I wanted to buy. The prices ranged from excellent to fair, and the range was quite good. So you might be interested in visiting, they're open seven days a week.