I don't think there's a cadre of must have books. The real work is in the reading of those books. Just one good magic book, if properly studied will yield huge gains in one's performance quality.
I think Hay's Amateur Magician's Handbook, Elliot's Classic Secrets of Magic and Expert Card Technique (all readily available and the first three magic books I ever found) will provide the dedicated student all he, or she, needs to begin well. All three are available at Amazon, even as we speak.
http://www.amazon.com/gp/offer-listing/ ... 193&sr=8-1
http://www.amazon.com/gp/offer-listing/ ... 241&sr=1-1
http://www.amazon.com/Classic-Secrets-M ... 304&sr=1-1
Nowadays with Giobbi available it should be even easier to become a more than competent card magician.
It isn't the books, it's the guy with the magic wand who has read ANY good books and absorbed the knowledge. Don't despair for want of good magic books, despair for you and me. We should be reading and assessing those great books and not worrying about anyone else. I'm going to go crack volume 3 of Giobbi, it is as far as I've gotten.