I was married in 2008. My now x-spousal will not communicate with me about filing a joint return for that year. How do I know what exemptions I can take (house, kids, etc) if I file separately and we haven't agreed on anything? How do I protect myself from him filing and claiming everything for himself?

Were you still married on Dec. 31, 2008?
With whom do the kids live?
What if any are the court agreements?

The kids (3) live with me 100% if the time. The judgement says that it is "anticipated" that we will file jointly in 2008. I have exclusive use of the house. In Lieu of alimony, he was ordered to pay the mortgage in the temporary order. He paid it for 6 months.
Thanks,

You are entitled to take the kids as your dependents, since the kids live with you and there isn't a court order to the contrary. Assuming your divirce was finale before Dec 31, you should be able to file as Head of Household, which will be better for you than filing as Single. If your divorce wasn't final, but you were "essentialy unmarried" you may still be able to file as HoH - post back if you want the details. As for the house deduction - if he paid the mortgage it seems only fair that he should get to deduct the interest and property taxes.