Obviously released ASDA exams are a must (particularly 91, 93, 98 and the new one released last month). If you are having issues w/a particular subject do a little research in your textbooks. I think the subject of implants was not covered well in any of the study materials and I'm not sure where to find the relevant info other than a textbook.
Also Tufts is a great resource.
I'm wondering if the Kaplan Q bank is worth it. Anyone?