I actually had one a few weeks ago. It was for my first choice unit, so I was nervous too...but they offered me the job!
It wasn't as unnerving as I thought it would be, though they did take a lot of notes. Some of what they asked me:
-Why did I switch to nursing from my previous career?
-Why this unit?
-Why should we hire you?
-What would your previous supervisor/co-workers say about you (strengths & weaknesses)?
-What do you expect from this position?
-Long & short term goals
-How would you handle conflict?
-Time when you had to think/act quickly?
They also asked about my nursing program
(what I thought of it, a little about my clinical experiences, how many pts I took at a time) and my previous career (it was in healthcare).
Any time I had the chance to give a solid example to back up an answer, I did it (times I'd gone above & beyond, an actual conflict I'd had & solved, situations that supported my strengths & weaknesses).
I had researched their hospital & unit beforehand so I was prepared and had questions to ask them, as well.
I knew they'd be making a decision quickly, so the next day, I sent a thank you e-mail to each person who had interviewed me.
You got the interview for a reason, so go in and show them that you're excited, willing to learn, flexible, and really want to be there. You'll do great! Good luck!