Yeah you can look at a variety of development issues in political science and sociology as well as of course policy. If you want to get on the public health side of things sociology or these "social policy" programs offered by sociology departments probably aren't a bad bet. These won't be wildly different from policy programs, I don't think. The advice, regardless PhD program is pretty much always that you should look at the recent working papers that the department's faculty are doing, and especially the sort of stuff the recent job market candidates are doing. You can hopefully triangulate that with the different focuses of the development institutions you'd be aiming at longer run, and try and track in a specific direction. So yeah I'd look at ag econ programs, policy programs (especially these), maybe some sociology programs who do lots of medical and development sociology (I don't know yet what development sociology is, but I suspect it's scarily statist and Marxian), and maybe some poly sci. That's vague, but Google is your friend here, and I think you've generally got the right idea. Good luck.