All of the question banks will let you have a free trial of some sort to help you get a feel for their site. I'd recommend choosing one that writes thorough explanations of the answers and has a system that allows you to query questions that you don't understand or appear to be incorrect (No question bank is perfect!). Take a look at ATPLOnTrack, ATPLQuestions, Aviation Exam and BGS for starters........other question banks are available ; -)