Although many refer to Jeff Sackman
's Math Bible as a advanced math guide, I would recommend it for beginners. I've been using this book to build fundamentals in math and to push my Q from low high 30s to low 40s. Later in the game I included Manhattan and 4gmat in an effort to push from 42 to high 40s.
Jeff Saackman's math Bible does not contain advanced material as sugested by many members of this forum, but is a great resource and provide really good coverage of 40 most tested concepts in GMAT. Friend of mine has to start her own preparation, she already got Q36 in real exam taken without any study. I think she is going to start with Math Bible and than continue with MGMAT, OG, 4gmat and than Powerprep, GMATprep and GMAT Focus, respectively. In 5 months I expect her to break into 48-49 territory.
My GMAT experience
My retake experience - GMAT dropped from 720 to 690 - advice for retakers
My TOEFL experience - 108