How Did You Prepare for this Interview?
This question is simple, easy to ask, and could yield a ton of great info. Listen for the candidate who loses their composure, showing they are lost at the notion of preparing. Listen as well for the candidate who describes their web-based research, their review of your published materials, the conversations they had with friends and associates who work for or with your firm, etc. What someone has done to prepare for their meeting with you can speak volumes for how they will approach the job for which they are applying.