Obviously, this answer depends on what you're interested in. As for myself, I'm quite interested in LISP and making compliators/interpreters for it. Therefore

Obviously, this answer depends on what you're interested in. As for myself, I'm quite interested in LISP and making compliators/interpreters for it. Therefore On Lisp and Lisp in Small Pieces are books I'd recommend. (No, I'm not going to tell you that LISP is going to change your life.)