If you must answer, something like
Well,when researching this position, glassdoor, payscale, and other sources suggest the range of pay generally is between $XX,XXX and $YY,YYY in total compensation
They almost assuredly know this information already. So all you do is tell them, "you can't low-ball me since I did research to know what my skill set is worth in comparable positions, I did research too."
Just don't use incorrect numbers...
Note this is "total compensation" not "salary" for reasons DJClayworth's answer talks about.
If you want to avoid even more and are decently assertive, try something like:
Well, it's a bit early in the process for this, I would rather first ensure a good fit before getting too much into the details of salary.
Note that if you are in an initial phone screen this might be harder to avoid because at that point you haven't convinced the HR person you are worth hiring. So whatever you say, make sure you make it clear you are not doing this because "I don't want to answer" but "I'm working with you in this process."