http://www.talkmagic.co.uk/ftopic11429.php
Download Craig's article. You'll see the two books he refers to as the 'Bibles'. He's right.
Mandrake is quite correct that Paul Brook's books are very good, but they are really not 'entry-level', and they aren't wide-ranging enough to qualify as 'Bibles'.
To give you a slightly different view, Bob Cassidy thinks that '13 Steps' isn't an essential read. He's right, in a way, but if you just want one book on mentalism rather than to amass a library, it's the one to get.