I agree with Simhan's suggestion. Choose a broad area of interest to you and then do some reading. It will show you some gaps or an area that you would like to explore further. If you are doing your internship with an organization, it's better to ask them what would be useful to them, or else you can choose for yourself.
I would suggest reading some HR magazines, which will give you an idea of what is currently going on, and then you can combine it with your interest. Finally, choose to research something in which you are really interested.
Best of luck.