At the end of the interview always comes that dreaded moment when the interviewer asks, "Any questions?"
Not asking questions can be taken as a sign that you are not interested or knowledgeable enough to ask questions.
If you really can't think of anything to ask, then get out of the danger zone by saying with conviction something like, "No, I think you answered just about everything I was going to ask you."
If you want to be able to ask a question when this awkward moment comes, however, here are a few suggestions:
"Where is the company heading in the next five to ten years? Is it planning new products/services/ventures?"
"There seems to be a lot of competition in this industry. Do you think this company is in a strong position to compete?"
"Do people tend to work here for a number of years once they're hired or is there a high turnover?"
"In what capacity did you first join the company? How has your career progressed?"
"Do you adopt new technology quickly? How old is your computer system?"
"What does the company look for in an employee?"
"If you could change one thing about this company, what would it be?"
http://www.abastaff.com/career/interview/askinter.htm