One of the (many) things I used to dread before interviews was what questions to ask my interviewer. I knew that coming in with nothing to ask made you look unprepared, but I never knew what I really needed to know about a potential job (other than a couple questions intended to prove I'd done my research). These questions are an amazing opportunity for you to collect information about different potential careers. Remember, job interviews are a two way street- you need to figure out that you want the job just as much as they need to figure out that they want you.
To help others through the interview question debacle, I've compiled a list of questions which target things that have surprised either me or my friends upon arriving at a new engineering job. A lot of this information may be included in the job description, so make sure to read it carefully and not for information which has already been provided to you. Note that this is most relevant for personal interviews, not technical interviews. If you have the opportunity to ask questions at the end of a technical interview it wouldn't be totally out of line.