I'm married to a Mexican and live in Mexico. How am I supposed to file: single? married separately? or what?

I've lived in Mexico first as single. My income comes through a US-based organization and so I've filed single for several years. But now I'm married to a Mexican (who therefore has no duty to pay US taxes), we still live in Mexico. How should I file? Single? Married Jointly? Married Separate? I'm not sure.