Speaking of The Eighth Tower, this is what my copy currently looks like:
Not wanting to mark up pages with notes, I'm using little sticky notes with brief comments I've written so I can go back and refer as I need to. And I'm not even finished yet.
This edition is the Signet paperback, New American Library/Times Mirror, Signet first printing, May 1977. (copyright John A. Keel 1975.)