The Card Magic of Nick Trost.

Card College if that counts as one... Since I assume it doesn't, maybe Mnemonica simply because it feels like it could take a lifetime to master everything in that book.

Alton Sharpe's - "Expert Card Mysteries" is a book that was very influential to me, as it was the first 'proper' card magic book I owned that wasn't full of counting or spelling tricks.

Great content by some of the world's best card men :- Larry Jennings - The Visitor, Open Travellers & Homing Card are all in there, Harvey Rosenthal - Cavorting Aces ( a favourite of Charlie Miller), along with contributions from other well known luminaries, such as Ed Marlo, Ken Krenzel, Roger Klause, Bruce Cervon, Paul Le Paul etc.

There are also a few unusual sleights and techniques taught, but the highlight was reading the material of lesser known magicians that was very good as well.

A Marlo book.

This would be my pick as well. But if it does not qualify since the book is not strictly cards, then I would choose "Card Magic" which is a book that contains all of the card work from Greater Magic. Great book for anyone that is not interested in the rest of the content in Greater Magic.