Webexams is good and one that I have used in the past, but I noticed that I started to get the same questions over and over after I while. I dont know of any other good sites with free questions, but if you dont mind spending a little bit of money, I would suggest Gleim's tests on CD. They are great.
Sporty's has free practice exams on their website. As a side note, when I took my private written a couple of weeks ago, probably about 80-85% of the questions were exactly as they appeared in the Gleim book, so that would be a good study tool as well if you don't have it yet.