Of course rental car companies are not going to volunteer this info, especially if they can get you to pay the additional driver fee, but for rentals within the states of California, New York, and Nevada the renter’s legal spouse is considered an Authorized Operator, and with permission from the renter, may operate the vehicle.
AVIS doesn't charge for a spouse anywhere in the US.
From their website FAQs, under Requirements for Renting, Can someone else drive the car that I rent?
The following individuals, if 25 years of age or older and in possession of a valid driver's license, may drive the car with the renter's prior permission:
•Renter's employer (while on company business);
•Renter's fellow employee (while on company business
•Renter's spouse or life partner.
The above additional drivers are considered "authorized drivers" and need not be present at the time of rental, nor do they need to sign an additional driver form.
I haven't verified, but I believe Hertz Gold and National Emerald members also don't get charged for a spouse.