I have been married for almost 4 years but never filed taxes with my spouse. I was wondering if I could file with my spouse now? When we got married we did not live together & separated about 2 months after the marriage. We have now reconciled & I want to know how should I file when I do my taxes. In the past I have filed as head of household but this past year I was not working that much due to all of the layoffs & my spouse was the one handling all of the bills & we moved in with each other. Please someone tell me what I can do.

If you are legally married you must file as either Married Filing Jointly (MFJ) or Married Filing Separately (MFS). You can not file as Head of Household unless you are unmarried, or are considered unmarried, meaning:
a. You file a separate return
b. Your spouse did not live at home for at least the last 6 months of the year
c. You paid more than half the upkeep of your home
d. Your home was the main home of your child, stepchild, or foster child for more than half the year
e. You must be able to claim an exemption for the child (unless the non-custodial parent is allowed to claim)

So for the preevious years you were probably OK filing as HoH since you were separated from your spouse (I am assuming you had custody of a qualifying child or relative during that time). But since you are back together now for 2010 you should file either as MFJ or MFS. For most people it is better to file MFJ, but it's always a good idea to run the numbers both ways and see what works best for you.