I've heard good things about "First Aid to the Match". I went with Iserson's myself though. Iserson's is a little bit dated, but I did find it be pretty comprehensive. Remember that Residency directors are a diverse group, and even within any one specialty, they will be looking for a different things in their applicants. If Iserson's doesn't answer what you are looking for, you will probably have to speak with the dean of your student affairs or a residency program director to get the answer.