For those looking for online services to help them study and obtain their Project Management Professional (PMP) certification, here is

 

PMStudy

Of course, most of their services are for a fee, but you can find some practice tests for free.

http://www.pmstudy.com/enroll.asp#PMP

I tried the 15 questions option, and it is well designed.  The explanation for the answers are useful to further learn and improve your results.

Take a look!