From personal experience, I'll give you two of my favorites.

First is not so much a question as a statement: "Ask me something." You could just as easily say, "Do you have any questions for me?" but I prefer it more directly, to prevent them from saying "No, not really."

What they ask you will tell you a great deal about how rehearsed they are, but also ideally what they are interested in. Do they ask about the benefits, about the work, about the business model? Do they ask about you?

Second is harder to describe, since it is very specific to my life as a computer geek, but depending on your industry I'm sure you could alter it accordingly. It goes something like this: "Have you ever had a project where you were so in the zone that you dragged yourself away from the computer at night, went to sleep thinking about what you were going to code the next day, and then woke up anxious to get back to the computer so you could pick up where you left off? You know what I'm talking about? I don't mean a death march, I don't mean where you turn into a zombie who hates his job. I mean that zone you get into where you're on such a roll that it's painful to break out of it. You know what I mean?" To date, every computer programmer question I've ever asked has said that yes, they know what I mean. "Good," I say, "Tell me about that project." At one job we used to call it the "passion" question. Tell me about a project you were passionate about.

The "good" ones end up sitting on the edge of their chair as they relive their story. The great ones jump out of their chairs and head for the whiteboard, without being asked. The mediocre ones have to stop and think about it, and you get the feeling that they could have picked any of half a dozen stories, but they never got very animated about it.

At the end of the day I'm most often interviewing people who will be colleagues, and I have to ask myself, "Would I like working with this person? Could I work side by side, disagree with, get into the occasional shouting match with, and still want to go have a beer after? Do I think that she's going to be as committed to the success of this job and company as I am?"

Oh, one more - another favorite is to pick a very real problem that has stumped you or your team recently, even if you haven't solved it yet, and ask the person to solve it. Even if they can't, it will a) give them a taste of what you work on, b) give you a chance to see how they think along those lines, and c) maybe give you some ideas about solving the problem yourself.

An interesting question is whether you can get the person to do actual work as part of the interview. Way back in high school I worked at a place that was hiring data entry people, and during the interview they would sit the person at a terminal and say "start entering." One girl, who'd never been told whether she'd be paid for that time, got up and left. A more recent and relevant example is the place I worked at that had interviewees write out - long hand - working source code. That was a good test, to see how much people cared about doing what they're told. If they think writing out source code is dumb, then that's fine - but if you refuse to do something like that just to get the job, how do I know that you're not gonna tell me something else is dumb and refuse to do it, after I hire you?

I run a business with 150 employees and we have a "blanket" form to fill out but this is not adequate enough. I find just talking about them,about their family and whatever things they are interested in. This lets there guard down and you get to actually talk to the person. Its very hard to see the real person unless you ask them things they are comfortable with and then they loosen up. Then the previous peoples comments are most honest not what they think you want them to say.

What were you doing before you looked for this job?
Why are manholes round?
What do you expect to get paid with your new job?
What were your responsibilities at your last job?
What are the major challenges that you encountered?
Why is your job rewarding?
What hobbies or interests do you enjoy outside of your job, and do any relate to your job?
What motivates you most?
What are your biggest accomplishments?
What is your biggest failure?
What do you like or dislike about your boss?
Who was your best boss, who was your worst boss, and why?
Why are you leaving your current job?
What have you been doing since your last job?

Really anything that is relevant to the position is a "good" interview question. Asking about past employment, general questions to get an idea of their personality/work ethic and experience are ALL very good questions. More important than a "good" question, are the "bad" questions. These are the questions that can get you sued...the following link has both examples of good questions, and questions to avoid.

http://www.jobinterviewquestions.org/

Ask them what they know about your company. You'd be surprised at how many people come into an interview with no clue about the company or position they're applying for. I think if someone has done their research and can concisely tell you what your company does, then it show their dedication.