I have 2 year lease agreement for renting a house from 8/21/09~8/21/11.
House was foreclose and sold at auction on 5/24/10.
The new landlord is asking me to move out by 8/31/10, but asking me to pay them rents for June, July, and August.
I know that I have right to stay here for 90days, but do I have to pay them rent for those 3 months?

It is August. Didn't you already pay the rent for June, July and August?

Why would you think you don't need to pay rent if you're still living there?