My husband & I are separated.. I am not listed on the deed to the house & he has it up for sale. What are my rights?

Generally, under Ohio law, all property acquired during the term of the marriage is deemed marital property. If your Husband wishes to show the real estate is premarital or separate property, the burden of proof is on him. If the property is both marital and separate and/or premarital, the burden of proof would be on each of you. In order to stop the sale, you need to file for divorce. If you decide not to file for divorce, you can nevertheless stop the sale by refusing to sign the dower release on the warranty deed that the escrow agent will want you to sign.
I recommend that you consult with an attorney regardign your specific rights based n the facts of your case. Please be aware that this answer to your question does not create an attorney client relationship. Rather, I have provided general information relative to your general question. Many more facts are needed to fully address your situation.