I've always enjoyed probability and stochastic processes (took two courses in stochastic models in undergrad, and a PhD level intro to stochastic processes course for my master's). Someday I'd like to go back to school, and most likely I'll study applied probability/stochastic processes. Now, the vast majority of work in this area these days seems to be motivated by quantitative finance; while I have nothing against this field, it is not really what I'm interested in. I took a course in accounting and one in engineering economics and was bored out of my mind.
Additionally, I still have no idea specifically what I want to research. This of course makes it hard to write a coherent personal statement for graduate school applications. I will be working for the next 3-4 years to pay off my loans, so I have some time to think about this. I work in revenue management, and the most interesting thing I've seen so far is a probabilistic overbooking model. That model isn't overly sophisticated but it's a cool example of using probability to maximize expected revenues.
Any ideas on areas to research (and books/references) would be greatly appreciated!