www.mba.com - This is the official GMAT web site. Lots of authentic information about GMAT on Test FOrmat, Registration, Books and software's for GMAT preparation.
www.gmac.com - This is the Graduate Admissions Council. You can find lots of GMAT statistics and lots of research, career oriented news about GMAT.
www.usnews.com - This site gives you the rankings of all top US universities
www.ets.org - ETS - Educational testing service administers the GMAT. Here also you can find authentic information about GMAT.
www.gmatclub.com - This is a community web site where lots of aspiring MBA students participate in discussions and help each other. Great web site to meet like minded people.
www.syvum.com/gmat - Find lots of free GMAT practice tests from this web site
www.gmatbuster.org - another web site with lots of GMAT information. Helpful in GMAT preparation
www.businessschooladmission.com - All about B-School admissions as the name suggests.