some online computer certification sites

http://www.expertrating.com/examlist.asp
http://www.brainbench.com/xml/bb/common/testcenter/freetests.xml#sponsored
http://www.ncsacademy.com/
http://www.expertrating.com
http://www.examsonline.com/HOME/
http://www.tamingthebeast.net/training/testing.htm
http://certification.about.com/cs/sampletests/a/practicetests.htm
http://www.e-learningcenter.com/free.htm
www.whizlabs.com