Who do you pay rent to when the landlord has passed and an executor has not been appointed?

The Estate of x (landlord's name).

I would set up a separate account and deposit your rent checks there. As soon as an executor is appointed you turn over the account to them.

Yes if there is no person appointed yet, set up a special account for this money, notify the heirs of this and then put the moneyin there

This may vary from State to State, from County to County, perhaps but in the two months between my husband's passing and probate the Attorney advised tenants to pay rent to his Estate and send the checks to me.

Again, this may vary from place to place but as soon as the Will was admitted to probate I was able to deposit the checks. I had no contact whatsoever with the tenants.

If you know who the likley heir/executor will be you can do what Judy suggests. Otherwise, I would do as I suggested.