My response isn't witty or clever, and you probably already know all of this but for those who don't here goes...
Żou want the best out of your applicants, your time, their time etc, so try to be relaxed and disarming right from the start. Save the "I'm super excited about this for the de brief with your superiors later".
I'm sure you know how bad the job scene is, and must know just how nervous these people will be, whether they show it or not. Some will want a job at any cost, watch out for the 'yes men'. You'll want to weed out as many of these and the unqualified asap!
I try to get them to relax by starting out with some light banter, address the nerves and dismiss them as unnecessary, find something in common etc in other words don't hammer them as soon as they sit down... Resist
Once they relax a bit, hopefully they'll get out of their heads and relax and open up enough for you to see what they're really like, if they have the skills and soft skills required for the position and if their personality will fit in with the company.....culture...
Ask about a specific problem they have solved.
Or my favorite: "why should I hire you?"
Who is prepared? Who knows all about the company and the position, who did their homework on the company?
Who is asking intelligent questions as opposed to the boring "how much is the comp plan" :/
I like the suggestion of open ended questions too. Also, I review the resume with the same technique of open ended comments and see if they catch on and complete the thought.
Maybe mention something on their resume (past job-experience-skill set etc) and see where they go with it.
Might be a good way of verifying what's written on the resume/cv vs actual real life experience. Pretty effective on catching the BS'rs who have prepared statements... Keep them thinking on their toes by not being predictable.
Ps. If you really want a nice docier on interviewing techniques and questions hit me up with a PM
Anyway, congrats on the assignment and responsibility! You'll do great!
Cheers
Jason