The most difficult question is always salary expectation. Having been employed with my previous employer for over 20 years and also in a higher paying industry, my salary was on the higher end for an executive assistant. I answered "while salary is important, it is not the most important thing for me. I am more interested in the total package of a company. I would prefer to fit into your company's pay structure." This allows me the opportunity to not provide an actual $ amount which could help get me to the next round. Unfortunately, sometimes they will follow up with, "what did you make at your last job?" Once I give the number, I'm always told the position doesn't pay anywhere near that amount. If I'm interviewing for a position in a different industry I then counter with, "I realize having worked in the financial industry, the salaries are somewhat higher and all I would ask is that I be paid a marketable salary comparable to a person with my experience within your industry.
The most unexpected question I was asked was, "what made my writing skills excellent?" That threw me and I'm still not sure if my response was adequate but I responded with, "In these times with communication being conducted mainly via e-mail, I have had to hone my writing skills in order to be effective in my job. The fact that my boss consistently asks me to respond to correspondence on his behalf indicates to me that my writing skills are up to par with his expectations. I personally think they are excellent but realize that is subjective.