Do You Have Any Questions For Me?
Asking good questions can reveal a lot of your personality and can be the most important part of the interview. Take some time to craft very personal, well thought-out questions that require more than a "yes" or "no" answer.
Don't ask questions that seem to be too assuming and that make you sound like you think you got the job. Don't try to focus on pay, benefits, and getting promoted. Focus more on what you can do for the company and not what the company can do for you.
Use your judgment during the interview on how many questions are appropriate.