Hi. I am a US citizen living outside the US with my non-US spouse. I file my Indv. Income Tax Return as 'Married filing separately', enter my spouse's name and SSS ( he worked in the US many years ago but NOT ANYMORE), and claim no exemptions nor any standard deductions ( since he claims me as a dependent in his own country, where he pays his taxes). Therefore, I always end up paying taxes to the US gov't. I have also been paying taxes for the past few years. This year, I even paid taxes on the small amount of social security benefits that I started receiving in 2009. Have I been doing the right thing? Do I have to write his SSN in the form and exempt myself?

You can file as married filing separately or as married filing jointly.
On the joint return both must report worldwide income. Your U.S. Tax Return: U.S. Citizen or Resident with Foreign Income

Thanks for your reply and info,MTE.
It seems that I was doing myself injustice by not claiming any exemption ( not even for myself) nor any deductions. My husband is a non-US person ( read : a foreigner that has nothing to do with the US), even though he had an SSN. When I amend my 1040A and claim the self-exemption and standard deduction, could I skip writing his SSN? What should I write instead?

Spouse is never a dependent.
You can amend you tax return that is file Form 1040X and claim your own exemption.