If you are working with a recruiter and he/she got you the interview, you should ask them what salary range the firm stated for the position; and then share the high end of that range. This way you can negotiate toward the middle of that range, if necessary. If you’re applying directly and don’t know a range, it’s advisable to ask for something slightly north of what you’re currently earning, maybe 10% to 15% higher. This is not a "frothy" market for the jobseeker right now, and you don’t want to price yourself out of contention before you’re even selected to interview.
Always go to an interview prepared to answer this question. Do your research. Look up the position you are hiring for on wwwsalary.com. Find out what the average pay is for the position for your educational level and level of experience. This way you can answer "Based on my research, I’ve found that the starting pay for this position for someone with my education and experience is between (blank) and (blank) and I’m comfortable with that." This way you showed you did your research, you came prepared, you still answered the question without committing to an exact number leaving the door open for negotiations.