If you're asking about me personally, I work on artificial intelligence; an (out of date) research statement can be found here. My research also sometimes branches out into nearby fields such as statistics, program analysis, and theoretical computer science.

More generally, if I found myself switching fields then some major contenders would be bioinstrumentation, neuroscience, materials science, synthetic biology, and political science. Of course, the particular choice of problem within a field is in many ways more important than the field itself, so in some sense this list is just cataloguing my biases.