I personally found Airquiz to be a great help when I was taking my exams (January 2011), more for the questions I got wrong than for the ones I got right, as it encourages you to re-visit the topics.
Your question prompted me to take an AirQuiz test again, to re-familiarise myself with the style, which I think is good, but definately not identical to the actual exams.
If you are using the Jeremy Platt books, the mock examinations in there are good as well.