Card College is the gold standard for card magic. Several volumes. Very clear illustrations. Pricey. There is also a DVD with the book's text and videos.
The Royal Road to Card Magic is much shorter, much cheaper, and also a classic.
Erdnase is like the Genesis of the card magic canon. While it has an important & worthwhile place on any cardworker's bookshelf (Dai Vernon basically considered it the bible), there are some newer & more modern treatises a little more accessible in terms of language, descriptions, illustration, and just overall instruction. The multi-volume Card College series by Roberto Giobbi comes to mind.
Card College by Roberto Giobbi is pricey but provides excellent instruction. If you don't mind reading older, more formal language (though not as old as Erdnase!), The Royal Road to Card Magic by Hugard and Braue, and its sequel Expert Card Technique, cover more material than Giobbi at a fraction of the cost, albeit with slightly less attention to the subtleties of finger position.