Anything that you find worth researching
Can you think of any interesting research topic?
What I find interesting you may not. Right now I could use some info on water run off and the effects of erosion. (We have had two rainstorms over with over 4 inches of rain in a short period of time and my backyard is a mess!)
I think research about Apoptosis nowadays is quite popular, maybe you should have a try,
Reversing/halting ageing process.
Radio Telescops of the world.