E. L. Easton Quizzes
http://eleaston.com/quizzes.html

Funbrain Quiz Lab
http://funbrain.com/
http://www.funbrain.com/teachers/signup.html

Discovery School's QuizCenter 

http://school.discovery.com/quizcenter/quizcenter.html  

HPRTEC's QuizStar
http://quiz.4teachers.org/index.php3  

Quia
http://www.quia.com/

Online Quizzes
http://jawbone.clarkston.wednet.edu/pages/classwebs/webservices.htm#quizzes
The Clarkston (Washington) school district provides a comprehensive list of sites for both online quizzes and activities.  

HostedTest.com
http://www.hostedtest.com/
subscription

12Teach.com
http://www.12teach.com/  

Tutor Center
http://tutorcenter.com/advscripts/default.asp
 

Eleaston.com
http://eleaston.com/quizzes.html

Create Your Own Multiple Choice Test
http://interactivetest.com/  

QuestionBuilder.com
http://questionbuilder.com/
 

Hot Potatoes
http://halfbakedsoftware.com/
(download software to create free quizzes)
 

Question Builder
http://landmark-project.com/classweb/tools/question_builder.php3
question_builder.php3