I have been using the COMLEX Qbook in prep for level 1. It is an amazing book and I love how the detailed answers to right and wrong questions allows me to learn more than what was presented in the case question. I have also found that the COMLEX qbook questions are identical to the USMLE qbook questions. The only difference is there is an extra 100 OMT questions. The reason I bring this up is that it allows prep for both the COMLEX and the USMLE at the same time. No need to get a separate qbook for the USMLE. Also the Underground Clinical Vingettes I heard are an excellent resource. Have you (anyone) tried those yet?