i like asking the person to describe a challenging situation in a previous job and how they handled it.

one of the strangest interview questions i was ever asked was what search engine i used.

Tell me about your first job.

It is amazing what people remember, how it formed their opinion of working, and where it may have led them after the job was over.

The one thing to remember about interview questions is that they must have relevancy to the job.  Asking broad questions can lead a candidate to give you information that you don't necessarily want to hear (i.e. married, children, disability, etc). If you hear this and then don't hire the candidate, they could potentially come back and say that they told you this information and that is why you didn't hire them, leading to trouble.

One of the things I like to do is ask a question that might be a little beyond the experience level of the group of candidates I'm interviewing, but still relevant to the position. 

 For example I asked a question for a supervisor position in a call center about managing FML. Much of the pool of candidates were new supervisors, or folks that were in supervisor assistant positions and looking to move up.  I didn't do it to be mean to the group.  My thought is that everyone encounters things in their position that stump them.  It's good to see how a candidate would think through getting the information when they feel pressured to know it all ready.  It helped identify people who would say anything to fake it, instead of researching the right answer.

One of my favorite questions to ask is "How have you improved your current/past position?"

This tells me a lot about a person's initiative. 

I always ask about his/her past experience or a situation that he faced and how did he deal with it. This experience is related to competencies like Service Passion, Stress Tolerance , Ethics......etc.