Wow, that's a pretty neat set of degrees you have, all of which would be applicable to global health in different ways.
You could, of course, serve as a nurse with doctors without borders (if you have enough professional experience, 2 years I think . . .)
www.doctorswithoutborders.org, or as a nurse in another aid organization. Direct care of patients and/or managing a clinic, or you could work on a public health research project out in the field. These options would require you to put your US nursing career on hold for a while, though you could always do a week here or there. You could also look at being a travel nurse, though this might not necessarily involve working with people in developing countries.
One suggestion is that you figure out what type of patients you like working with, or what type of disease entity interests you. Does studying and working to solve maternal malnutrition interest you? Or perhaps malaria? You could research, or you could go the patient care route, or a combination. There has been a certain demand for nurse researchers, though that might take a little bit more education, I'm really not sure about that route.
Global health is such a broad area, and it also encompasses issues and certain people in the United States. I know that you could probably work on an indian reservation, and perhaps get loans paid off as well, which would give you an introduction to a different culture facing difficult issues like diabetes, alcoholism and high unemployment.
Here is a link to some global health blogs:
http://lvntobsn.org/2010/top-50-international-health-care-and-nursing-blogs/
