What are your favorite old (pre 20th century) books?

As a small publisher, I'm often on the lookout for books to reprint. Some, like David Garrick ( a href="http://amzn.com/1441452206" rel="nofollow"http://amzn.com/1441452206/a ) , I do out of my own love for the text. What are old some books you fellows love?