Info on medical missions

In the next couple years, I really want to do a medical mission, up to probably 4 weeks. Preferably in Central America, as I also want to take this opportunity to immerse myself in Spanish in order to improve my conversational skills.

Anyone know of any reputable agencies?
Medecins sans frontieres (Doctors Without Borders) has a good rep and will always be happy to interview someone who's ready to hit the ground running (i.e., not students or new grads).

Yeah, I would LOVE to do something with them, but it seems like all of their missions are in French-speaking countries. I seem to recall that all of their trips are longer term than I could do (I think I recall that 3 months was the shortest, but I might be mistaken).Just looked....9 months is the shortest commitment. Dang, they do have some work in Mexico and Central America.

International Red Cross?Peace Corps?Just thinking out loud ...

Just a thought, but....Red Cross takes nurses to work in under-served areas of THIS country, too. I would have no doubt you could get yourself assigned to an area that is primarily Spanish speaking, and is also American. Much can be done right here at home