Official GMAT Site
GMAT.com: For registration, taking the test, GMAT bulletin, etc.
GMAT Preparation Sites
Kaplan: Classroom and online coaching
800score: Online and downloadable prep package
Crack-GMAT: Downloadable prep package
Prep.com: Live GMAT Training - Toronto Canada
GMATScore: Downloadable GMAT tests and subject lessons
Manhattan GMAT: Exclusive GMAT prep company offering online study programs and classes in select US locations.
Regional GMAT Preparation sites
GMAT preparation course in Eastern Europe
Live GMAT Training - Toronto Canada
Other MBA related sites
MBAinfo.com - The world's most comprehensive source of information on MBA programs.
MBAcenteronline.com - MBA articles and interviews with MBA recruiters.
Directory of Education and Career Articles - Research colleges that offer the degree you want, in the areas you want to live.
Study Abroad - with InternationalStudent.com, the premier study abroad website!
Edvisors.com - The Online Education Resources Directory