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.
Hugard and Braue are, again, totally canonical. (Almost sort of analogous to Thompson & Ritchie's published works on C/Unix, but for cards...sort of ;) They're cheap and easy to come by for <$10 each, and I agree that pound-for-pound, you're going to get more effects from them than anywhere else.
I do think for a serious beginner right now, though, Giobbi is probably more appropriate. I would argue he offers considerably more detail on subtleties of handling and overall performance and in more accessible language which is important. It's kind of like you're getting the best of Erdnase, Hugard, Braue and so many of the greats who came after them in the 20th century distilled down to best practices with Giobbi's course. There's nothing wrong with taking it slow either. You don't have to get all the volumes at once. In fact, it would be better to spend a long time mastering each before buying and moving on to the next.
As a note, too, R. Paul Wilson did a rather decent DVD series of The Royal Road to Card Magic, which you can get for ~$60. The book is a useful reference, but actually -seeing- the sleights can be amazingly useful.
And as others have mentioned, if you do go to Erdnase (or get sufficiently hooked to just want a copy), there is both the Annotated Erdnase by Darwin Ortiz (which is pretty readily available), as well as Dai Vernon's Revelation book (not to be confused with the 'Revelations' series of DVDs), his own annotations on Erdnase ( http://www.mcmagicwords.com/books_revelation.html ).
Yes, yes -- start with The Royal Road. It's a fantastic place to start. Graduate to Card College if you can afford it; otherwise, Paul le Paul, and then dive in deep with Buckley's Card Control. If you're still hungry after that, you and Erdnase deserve each other.
