GMAT http://www.gmac.com/gmac
GREhttp://www.ets.org/gre/
LSAThttp://www.lsac.org/LSAT/about-the-lsat.asp
MCAThttp://www.aamc.org/students/mcat/
Praxishttp://www.ets.org/praxis1/
To help prepare for all of the above exams: http://www.testprepreview.com/