The GMAT® -A source of online material for taking the test required for entry into most MBA programs.
GMAT Prep Course -ebook
How to Pass the GMAT: Unbeatable Preparation for Success in the Graduate Admisssion Test -This ebook lives up to its title, an excellent place to start preparing for the test.
NOVA's GMAT Math Bible -Study for the math portion of the GMAT using this ebook.